"A number of search warrants" are expected to be served later in the day, district attorney's office spokesman Larry King said.
Weintraub said it seems foul play was involved, but would not say more about the case or whether the authorities have a suspect or at least a person of interest subject to questioning.
He asked "for patience and prayers". "We've been treating this from the outset as a criminal investigation, and nothing has deterred that to this point".
"Right now, the focus of the investigation is to determine their whereabouts, and if we can bring them home safely", Weintraub said.
It is "all hands on deck" until the investigation is complete, he said. The other three men are identified as: Tom Meo, 21, of Plumstead, Pa.; Dean Finocchiaro, 19, of Middletown Twp.; and Jimi Tar Patrick, 19, of Newtown.
The district attorney went through the list of names to "dispel rumors", he said.
Bucks County District Attorney Matthew Weintraub held a press conference late Monday morning, asking anyone for any information to come forward and that the matter is being treated as a criminal investigation.
"I just want them to be found", King said while pointing to a police barricade at Aquetong Road and U.S. Route 202 near the search area.
Patrick has been missing the longest and police say no one has seen or heard from him since 6pm on Wednesday.
"He has had no contact with his family or friends and he has not shown up for work - all of which is not normal for Jimi", law enforcement officials wrote. Clark says that her family is offering a reward for information and that her son is a diabetic.
Sturgis' vehicle - a 2003 Nisan Altima with Maryland tags - was reportedly found in the Peddlers' Village parking lot in Solebury, according to the Intelligencer of Doylestown. Another vehicle connected to one of the men was also located in that area, the newspaper said.
Finocchiaro was last seen about 6.30pm on Friday entering a vehicle on Hampton Drive.
The prosecutor said authorities are trying to confirm reports the four knew each other.
Patrick has been described by police as a white male about five-foot, ten-inches tall, weighing about 150 lbs. and he was last seen wearing a polo shirt with a multi-colored design. "He is 5'9", 150 pounds and has brown hair and hazel eyes.
Another update from Weintraub is expected at 3:30 p.m.
NBC Philadelphia reports that Sturgis and Meo became friends while they worked for Sturgis' father, Mark Potash's, construction company.