Image copyright Bucks County District Attorney"s Offic Image caption The missing men. From left: Tom Meo, Dean Finocchiaro, Jimi Patrick, Mark Sturgis

Authorities are searching for four young men who vanished over a two-day period in a wealthy Philadelphia suburb, and say foul play is suspected.

Pennsylvania officials announced a person of interest on Tuesday as search crews focused on a vast farm owned by the man's parents.

Cosmo DiNardo, 20, was identified and also arrested on an unrelated weapons charge, but later released on bail.

Officials say his arrest was not linked to the criminal investigation.

"I want to be very careful to stress that he's a person of interest," said Bucks County District Attorney Matthew Weintraub, explaining that he was not currently considered a suspect.

"Sometimes the chasm between a person of interest, and being a person that is actually accused or arrested, and certainly convicted of a crime, is so wide that we never cross it," he added about Mr DiNardo.

Court records show Mr DiNardo was charged with possessing a shotgun despite having a history of mental health issues, including involuntary commitment.

Image copyright ABC Image caption It may take days to sift through the property, investigators say

Search crews using heavy machinery, metal detectors, and cadaver dogs have been scouring the Solebury Township 68-acre farm - about 40 miles (65km) north of Philadelphia.

News helicopters have been hovering overhead broadcasting the workers tearing up concrete and sifting through dirt.

Jimi Patrick, 19, was last seen on Wednesday evening one week ago and was reported missing after he did not arrive for work the following day.

Mark Sturgis, 22, Thomas Meo, 21, and Dean Finocchiaro, 18, were each last seen on Friday evening.

Image copyright Bucks County District Attorney Image caption Cosmo DiNardo, whose parents own the farm being searched, was arrested on unrelated charges

Officials have not yet said what connections the men have to each other or if they believe them to be alive.

Sources tell US media that a ping from a mobile phone belonging to one of the men led investigators to the farmland property.

Cosmo DiNardo was freed after posting 10% of a $1m (£775,000) bail. Authorities had on Monday re-filed weapons charges against him that had already been dismissed in May.

The man's parents, Antonio, 46, and Sandra DiNardo, 47, have been subpoenaed to appear before a county grand jury on Thursday, and have had their mobile phones seized, Fox News reports.

The FBI has been called to aid in the investigation, the district attorney said.