By Madison Park

CNN

(CNN) -- Four young men in Pennsylvania disappeared last week in a baffling series of events that have authorities suspecting foul play.

Local and state investigators, as well as the FBI, are involved in a massive search for the missing four men in an area north of Philadelphia.

Jimi Patrick, 19, of Newtown Township, went missing on Wednesday. The remaining three, Tom Meo, 21, of Plumstead Township, Mark Sturgis, 22, of Pennsburg, and Dean Finnochiaro, 18, of Middletown Township were last seen Friday.

Patrick was last seen Wednesday 6 p.m., and was reported missing the next day after he had no contact with friends or family, and didn't show up to work, according to the Newtown Township Police Department.

Meo and Sturgis had been last seen together Friday night near the Doylestown area in Bucks County, reported CNN affiliate KYW. Sturgis' father had said the two are friends, according to the station.

Finocchiaro was last seen Friday around 6:30 p.m., getting into a vehicle and hadn't been seen or heard from since, according to the Middletown Township Police.

Authorities have information that the four men know each other, said Bucks County district attorney, Matthew Weintraub. But he added that they were working on confirming that.

When asked if foul play was involved, Weintraub said, "It sure would seem so."

"We've been treating this from the outset as a criminal investigation and nothing has deterred that from this point," he said at a press conference Monday. But he said he couldn't share more information at this time.

Authorities were searching a massive, rural property in Solebury Township Monday. Search and rescue dogs, and backhoes arrived at the property, as seen by CNN affiliate KYW.

"The leads are incredibly hot, they're fruitful. We're making great progress. But there's so much more work to do," Weintraub said.

When asked whether he thought the missing men were alive at the news conference, Weintraub replied, "I hope and I pray that would be the best outcome. I just have to go wherever the evidence takes me. I don't know the answer to that."

Another press conference is expected Tuesday, 11 a.m. ET.