Laundrie's family told police he left home with his backpack Tuesday and told them he was going to the reserve, North Port police spokesperson Josh Taylor said Saturday.
Laundrie returned to North Port, Florida, without Petito on September 1, according to police. Officials later found the van the couple had been traveling in at the home Petito shared with Laundrie and his parents in North Port.
Police visited the home after Petito was reported missing, but Laundrie's family refused to talk and instead gave authorities the information for their attorney, Taylor said earlier this week.
The home was searched Friday evening, when Laundrie's family told police they had not seen him for days. Laundrie family attorney Steven Bertolino said Friday that Laundrie's whereabouts "are currently unknown."
Richard Stafford, the attorney for the Petito family, said in a brief statement sent to CNN, "All of Gabby's family want the world to know that Brian is not missing, he is hiding. Gabby is missing."
On Saturday, the FBI said the search for Petito included ground surveys being conducted in Wyoming's Grand Teton National Park alongside the National Park Service and local authorities.
Laundrie search continues in 'vast' nature reserve
Before efforts were suspended Saturday evening due to darkness, 50 law enforcement officers from five local agencies and the FBI conducted their search for Laundrie in the "vast" Carlton Reserve in Sarasota County, Florida, police said.
The search effort included the use of drones and bloodhounds who used articles of Laundrie's clothing taken from his home to get his scent, Taylor said. Police initially focused their search on a nearby park about 200 acres large before expanding out to the rest of the reserve.
Police believe the vehicle Laundrie was driving may have been at the reserve too, but has since been returned to the Laundrie's home.
Laundrie has an "enormous amount of pressure" on him to provide answers to what's going on, Taylor said Saturday.
When asked why Laundrie's family didn't tell police of his whereabouts until Friday, Taylor said, "that's a great question."
"You know we've obviously been trying to reach the family to get answers in this case since (last) Saturday," Taylor said. "The first time that we've had any in-depth conversation with them was (Friday) when their attorney called and said the family was concerned about Brian's whereabouts."