Where is Brian Laundrie? Report of possible sighting on the Appalachian Trail

The search for Brian Laundrie is expanding as the FBI investigates new tips of possible sightings. The latest comes from a hiker on the Appalachian Trail who tells FOX News he spoke with a man he's convinced is Laundrie.

"I'm absolutely 100 percent sure that was the guy. My heart was thumping," hiker Dennis Davis told FOX News.

Davis described to FOX News the moment he pulled up next to a man in a white truck he believes was in fact wanted fugitive Brian Laundrie, the only known suspect in the Gabby Petito case. It was around 12:30 Saturday morning near the Tennessee - North Carolina border.

"I started talking with the gentlemen. I could tell right away. He wasn't, something wasn't right with him," Davis said.

After the man drove off, Davis looked at photos of Laundrie on his phone. Convinced it was him, he called 911 and the FBI.

"I'm telling you this was the guy," Davis said.

RELATED: ‘Grabbed me with his nail’: Gabby Petito describes Utah fight with Brian Laundrie in newly-released bodycam

Meanwhile, the Petito family is taking to Twitter. Gabby's mom Nicole Schmidt tweeted Saturday, writing quote, "Mama bear is getting angry! Turn yourself in! @JosephPetito agrees."

While frustration may be building over the search, former FBI special agent and USF professor of criminology Bryanna Fox says law enforcement may know more than they're saying.

"When the FBI or local law enforcement are conducting investigations, keeping their cards close to their chest is integral to making sure the integrity of that investigation is protected," Fox said.

RELATED: How Brian Laundrie's behavior could provide clues about his disappearance

Some of biggest questions still out there: What exactly did the Laundrie family know? And when did they know it?

"There's this period of time before Gabby was reported missing when the Laundrie family was together. Obviously Brian is now missing. If they did anything during that period of time to help him flee the vicinity of the county, the state or the country, they certainty could be facing charges," criminal defense attorney Alex Little told FOX news.

The Laundrie family attorney says Brian's parents don't know where he is, adding in a statement any accusations that they helped flee the FBI are "just wrong."