Video above: Brian Laundrie's father joins the search for his son Thursday

As the search for Brian Laundrie continues in a Florida nature reserve, police said Friday that they have yet to find any physical evidence of Laundrie within the sprawling wilderness area.

Laundrie, whose fiancé Gabby Petito was found dead in Wyoming nearly three weeks ago, has been the focus of an intensive search in the Carlton Reserve near his family home in North Port, after his parents told police he planned to hike there.

North Port police spokesman Josh Taylor told CNN's Randi Kaye that although nothing linked to Laundrie has been found inside the reserve, their efforts will continue there until they have better information.

North Port police did confirm this week that an abandoned vehicle notice was placed on a Ford Mustang belonging to the Laundrie family on Sept. 14 outside a park that serves as an entrance to the reserve.

The parents, Chris and Roberta, went to the park that day looking for their son and saw the citation, according to Laundrie family attorney Steve Bertolino, a day after they say Laundrie told them he was headed for the reserve. His parents brought the vehicle home on Sept. 15.

The search has been prompted entirely by information from Laundrie's parents, Taylor told CNN, and while the police department has received numerous tips from the public, police say none have panned out so far.

Laundrie has not been charged in Petito's death, but he is the subject of a federal arrest warrant for unauthorized use of another person's debit card in the days after she last spoke with her family.

Police say Laundrie was under surveillance before he disappeared

Petito, whose body was discovered Sept. 19, was reported missing eight days earlier by her family who had not heard from her since late August.

When police, as part of the investigation into Petito's disappearance, went to the Laundrie family home on the night of Sept. 11, he was not seen and there was no opportunity to speak with him, Taylor told CNN.

While Laundrie was not wanted for arrest at the time, he was being surveilled by police — as best authorities could do so legally — before he disappeared, Taylor told CNN, and authorities say they never spoke with Laundrie before he went missing.

On Sept. 17, when police spoke with Laundrie's parents after they reported him missing, they refused to address Petito's disappearance or answer any questions about her, which police described as "odd," Taylor said. Laundrie's parents, who had their lawyer on speakerphone, would only speak about their missing son.

Laundrie and Petito had ventured on a summer road trip to western national parks, yet Petito was last seen in late August in a Wyoming restaurant and Laundrie returned home to Florida alone on Sept. 1.

Nearly a week after Laundrie came back, he and his parents went camping for a brief stay at a site around 75 miles from their home, attorney Bertolino told CNN.

In late September, Laundrie's parents released a statement through their attorney, saying, "Chris and Roberta Laundrie do not know where Brian is. They are concerned about Brian and hope the FBI can locate him. The speculation by the public and some in the press that the parents assisted Brian in leaving the family home or in avoiding arrest on a warrant that was issued after Brian had already been missing for several days is just wrong."

Father participated in search this week

Chris Laundrie was seen Thursday morning entering the Carlton Reserve, after being asked by law enforcement to accompany them on their search, according to Bertolino.

"Chris was asked to point out any favorite trails or spots that Brian may have used in the preserve," the attorney said. Though the family provided what information they knew earlier, "it is now thought that on-site assistance may be better," he said.

"The preserve has been closed to the public and the Laundries as well but the parents have been cooperating since the search began," Bertolino said.

"There were no discoveries but the effort was helpful to all," he said.

Police on Thursday denied that a campsite had been found in the reserve during earlier search efforts. That confirmation came after a source close to the Laundrie family told CNN they were informed by investigators that police had made a discovery. The source on Thursday insisted that the Laundrie family had been told a campsite had been found.

"Is it possible that they thought that there might be a campsite out there or something they may have seen from the air, but when they got on the ground that's not what it turned out to be? Sure, I think that's a possibility," Taylor, the North Port Police spokesperson, said. "Bottom line is that investigators are telling me that no campsite was found out there."

As the search continues, Laundrie's parents believe he is still in the reserve, Bertolino said, and as a result, any public call they made for him to surrender to authorities would not reach him.

"In short, the parents believe Brian was and still is in the preserve so there was no reason to issue a plea on media that he does not have access to," the attorney said.

As the search for Brian Laundrie enters its second week, officials are scaling back their massive efforts to find him in a Florida nature reserve in favor of a more targeted approach.

Since he went missing on Sept. 17, federal and local police have focused their tracking efforts at the Carlton Reserve, a 25,000 nature preserve near Laundrie's North Port, Florida, home.

But on Monday, a North Port Police spokesperson confirmed to USA Today and Fox News that the FBI — who is leading the search — would now base their search efforts on "targeted based on intelligence."

"I don't think you're going to see those large-scale types of efforts this week," Taylor said, according to USA Today. "Hopefully, water will lower in areas hard to currently access."

Gabby Petito's family is holding a press conference on Tuesday. Watch live below.

NBC News and Fox News report that FBI agents have also asked Laundrie's parents for some of their son's personal items in the hopes of conducting "DNA matching."

At a press conference on Tuesday, an attorney for Petito's family criticized Laundrie's family for their continued silence on their son's whereabouts and asked Laundrie to turn himself in to law enforcement.

"The Laundries did not help us find Gabby. They sure are not going to help us find Brian. For Brian, we're asking you to turn yourself into the FBI, or the nearest law enforcement agency," attorney Richard B. Stafford said.

Laundrie is listed as a person of interest in connection with the homicide of his girlfriend, travel blogger Gabby Petito. The two were on a cross-country road trip in a converted van to Utah and Wyoming when Petito went missing in late August.

During their road trip, police in Moab, Utah, encountered the couple after receiving reports of a domestic dispute. No charges were filed after Laundrie and Petito told police they would spend the night in separate places.

Petito's parents say they last spoke to their daughter on Aug. 25. At that point, she told her family she and Laundrie were in Grand Teton National Park in Wyoming.

Laundrie returned to his Florida home without Petito on Sept. 1. She was declared missing on Sept. 11. At that point, police attempted to speak to Laundrie, though he declined to cooperate with the investigation.

After a week-long search, Petito's body was discovered near Grand Teton National Park on Sept. 19. The manner of her death has been ruled a homicide, though coroners are still trying to determine her cause of death.

During a Sept. 16 press conference, police said they were aware of Laundrie's location. However, police said Laundrie had gone missing a day later and began a massive search effort to find him.

NORTH PORT, Fla. — Officials in Florida will resume the search for 23-year-old Brian Laundrie on Wednesday, a day after the FBI confirmed that remains found in Wyoming were those of his fiancée, 22-year-old Gabby Petito.

As of Tuesday, the FBI is the lead agency in the search for Laundrie, who remains a person of interest in Petito's disappearance and death.

On Monday, the North Port Police Department called off the search for Laundrie in a 25,000 acre stretch of Carlton Reserve in Sarasota County.

"At this time, we currently believe we have exhausted all avenues in searching of the grounds there (Carlton Reserve)," a spokesperson with NPPD said in a statement Monday. "Law enforcement agencies continue to search for Brian Laundrie. More updates when available."

However, the FBI resumed the search on Tuesday when they took over the case.

Authorities are now searching an area about 30 minutes from the initial ground of Carlton Reserve that police searched over the weekend.

Close to a dozen agencies are aiding in the search for Laundrie, including the North Port Police Department, the FBI, the Florida Wildlife Commission, sheriff's offices in Sarasota, Lee and Charlotte counties and police departments in Sarasota and Venice. K9 search and rescue teams are also assisting in the search.

Law enforcement is well-equipped to conduct its search.

"ATVs, UTVs, we have multiple drone operators that have been sent out in numerous teams, so we'll mix the resources and deploy them out so if they encounter flooded areas or terrain they can't access with these wheeled vehicles, we'll deploy our drones directly out into the wooded areas," Officer Joe Fussell with North Port Police Department said.

While authorities have several tools to help them in the search, tough terrain and wet weather have hindered the investigation.

North Port Police said the Carlton Reserve is a vast and unforgiving location, with water waist-deep in many areas. Crews are having to wade through gator and snake-infested swamps and flooded hiking and biking trails.

"Terrain is very difficult," Fussell said. "Essentially, 75% of it is underwater, and other areas that are dry, we're trying to clear. We are expecting to get wet by the end of the day and check the entire area for Brian Laundrie."

Authorities are using bloodhound dogs in the search. However, a former FBI agent who has worked in finding people in extreme environments said the amount of water in the area makes the search difficult for the dogs.

"They lose the sense that they're unable to continue tracking that scent," former FBI Special Agent Brian Kensel said. "I understand a few days ago; law enforcement did pick up some clothing, pieces of apparel from Brian Laundrie's house for that very purpose before they started the search yesterday, I believe."

When asked why the search was called off on Monday but resumed the very next day, Kensel had the same question.

"I saw that. I saw the announcement last night that we feel we've exhausted all methods — so, means — to search. And then something obviously changed overnight in terms of the information that was developed," Kensel said.

There have been reports that Laundrie was spotted in Alabama and the panhandle of Florida. However, authorities said that after further investigation, those claims did not hold true.

The Sarasota County Sheriff's Office released a statement via Twitter addressing rumors that Laundrie had been taken into custody.

Despite rumors on social media this evening, #BrianLaundrie is NOT IN THE CUSTODY of our agency at this time. We can confirm we have received reports of “suspected sightings” however, none have been accurate. pic.twitter.com/MrW4bKwuc2

— SarasotaSheriff (@SarasotaSheriff) September 22, 2021

This story was originally published by Vanessa Araiza on Scripps station WFTS in Tampa, Florida.