Pennsylvania state police suggested Monday that 21-year-old Matthew R. Royer, missing since leaving Rhode Island on Thursday, might have decided on his own to detour from returning to his Montgomery County home.

"While it may be a voluntary move on Matthew's part, we are still expending all resources in this investigation to locate Matthew," said Trooper Morgan Crummy, a spokeswoman at the Skippack barracks.

As that possibility took shape, his mother made a tearful plea for her son to contact his parents.

"Matthew, if you can hear this - no matter what the circumstances are - your friends and your family, we all love you," his mother said Monday afternoon at a news conference in front of the barracks. "We're here for you. Please contact us, call home. We will come anywhere, anyplace, anytime for you. We are here for you. We love you and miss you."

Authorities were poring through dozens of leads on the whereabouts of Royer, a Perkiomen Valley High School graduate, who texted his mother on Thursday that he was leaving his apartment in Narragansett, R.I., to return home for the summer.

His parents were away over the weekend but rushed to their Collegeville home when they learned their son had not shown up for his job at the Skippack Golf Club.

At that point, they began tracing his path from Rhode Island and learned he was last seen on a video from a security camera at 2:05 a.m. Friday at a Sunoco station on Route 100, about a 30-minute drive from his home.

State police said this morning that a witness who learned of Royer's disappearance through the media reported seeing his silver 2008 Chevrolet Cobalt 11 hours after the previous sighting, at Routes 501 and 422 in Lebanon County, more than an hour from his home.

Crummy said later Monday that police were still trying to verify that report and "dozens" of other leads they had gotten since publicizing that Royer was disappeared.

Royer lived about a 20-minute drive from the University of Rhode Island. Earlier reports said he was in the pharmacy doctoral program there, but Royer dropped out at the end of the fall 2012 semester, university spokeswoman Linda Acciardo said.

He did not take classes in the spring semester, though he is still registered as a student at the university, Acciardo said. He began attending the school in the fall of 2009.

"We have been in touch with the family" and have spoken with his parents several times, she said. "We're deeply concerned about his welfare and are looking for a good outcome to what appears to be a difficult situation."

Acciardo added that staff in the pharmacy program who knew Royer said he was quiet, likable, and hardworking.

Waiting to hear what has happened with their son is difficult, Randy Royer, Matthew's father, said earlier Monday.

"It has been four days, and we're physically and mentally exhausted," Royer said. "Just get the word out to find our child."

Friends took to Twitter for help in finding Matthew.

Wrote one friend: "Matt Royer, we miss you, hope you're alright and everyone wants you to come home. We have a summer soccer league to dominate too!!"

Royer is 6-foot-1, weighs 160 pounds, and has brown hair and blue eyes. He last was seen wearing a dark-green golf shirt, khaki shorts, flip-flops, and a baseball cap. His silver Cobalt has Pennsylvania license plate GZR 9059.

The Narragansett Police Department and Skippack barracks are jointly looking for Royer.

Anyone with information about him can call the Skippack barracks at 610-584-1250.