Recently surfaced surveillance video from a business in the area taken the night before Tripathi disappeared shows a man fitting his description walking in the neighborhood. Police have not been able to say definitively it is the missing man, but the footage has encouraged his family.
"I do believe it is him," said Ravi Tripathi, 26, the missing man's brother. The close-knit family has traveled to Rhode Island, and the video, he said, gave them information to use in their search.
In the last two weeks, numerous law enforcement investigators, family, and friends have searched coffee shops, homeless shelters, soup kitchens, hospitals, and morgues. They have visited stores, neighborhoods, and hiked along Providence rivers at low tide.
"Every ounce of property within walking distance - a three-mile radius - had been covered," Sacco said, adding that authorities did not suspect foul play. He would not divulge the contents of the note found in Tripathi's room.
An FBI forensic analysis of Tripathi's computer, bank, and phone turned up no clues to his whereabouts.
"Sunny," as Tripathi is known, had taken a leave from Brown University, where he was studying philosophy. He was volunteering at a local library while deciding on his next step, Ravi Tripathi said.
His brother, who suffers from depression, was in constant contact with his family through calls, Facebook, or texts, he said. They last heard from him the night before he disappeared.
The "Help Us Find Sunil Tripathi" Facebook page has helped drive national attention to the case. It generated more than 1.2 million unique views in its first week, and, as of Friday, had more than 4,400 followers.
Volunteers plastered posters around Providence and at Philadelphia's 30th Street Station and at Regional Rail stations. Calls and tips have come in from South Carolina, Connecticut, Pennsylvania, Boston, and Rhode Island.
"It is social media that has taken [the exposure] to the next level," beyond anything his department could do, Sacco said.
He asked anyone who may have seen Tripathi to contact their local police department.
Contact Mari A. Schaefer at 610-313-8111, firstname.lastname@example.org, or follow @MariSchaefer on Twitter.