Cosmo DiNardo, 20, was taken into custody on Monday and charged with a firearms possession offense from February.
It was not yet known if DiNardo is suspected of having any involvement in the disappearance of the four men.
He is being held on 10% of $1 million bail.
DiNardo was taken into custody at a home in the unit block of Wayland Circle in Bensalem. It was one of the multiple locations being searched by authorities on Monday.
His family also owns a property on Aquetong Road that was searched on Sunday, and a farm on Upper Mountain Road near Route 202 in Solebury Township that was the scene of an active search on Monday.
Bucks County District Attorney Matt Weintraub said he believes foul play is involved.
"I sure believe there is," he said during a news conference on Monday afternoon.
Weintraub said the leads in this investigation are "very hot."
"We've been treating this from the outset as a criminal investigation, and nothing has deterred that to this point," Weintraub said.
But when asked why he believes foul play was involved, he said it was due to "information that I know that I can't share."
Chopper 6 was over the farm in Solebury Township, where a number of police vehicles and a mobile command center could be seen.
"We're not exactly sure what we're going to find there, but we're pretty confident that the investigation is proceeding in the direction we believed that it would," Weintraub said.
VIDEO: Chopper 6 over search scene in Solebury Twp.
The missing men are identified as Mark Sturgis, 22, of Pennsburg; Tom Meo, 21, of Plumstead; Dean Finocchiaro, 19, of Middletown Twp.; and Jimi Tar Patrick, 19, of Newtown.
Sturgis, Meo and Finocchiaro were last seen on Friday. Patrick was last seen on Wednesday.
Earlier Monday, the parents of Mark Sturgis confirmed his car was found at Peddler's Village in Bucks County. Sturgis' father also said his son was last seen with Meo.
The wooded area being searched is also near Peddler's Village.
Weintraub said it is believed all four men know each other, but investigators are working to confirm that information.
At this point, Weintraub said it is "all hands on deck" to find the four men. He could not confirm if all four are still alive.
"I can't say. We hope they are, but we need to go where the investigation leads us," Weintraub said.
For now, he is asking for the community's prayers.
"At this point I ask for your patience and your prayers for these four young men and let us do our jobs," Weintraub said.
Anyone with information is asked to contact investigators at 215-297-8201.