Over the weekend, the search expanded to Boston, Connecticut, New York, and Philadelphia, according to the university. The FBI has joined the investigation, Tripathi's sister said.
Tripathi had suffered from depression, but his sister said his condition had not worsened in recent weeks. A Facebook page set up to help in the search said "a note suggestive of suicidal intent" had been found in his apartment. But his sister said the note was short and vague and gave no hint as to what happened.
The night before her brother disappeared seemed normal, Sangeeta Tripathi said. He went out with Brown classmates on a Friday night and had tea. He spoke to his grandmother on the phone and texted with his aunt until late in the evening.
"There was nothing out of the ordinary," she said of her brother, an avid Eagles fan who played saxophone and belonged to a chess club. "It's so hard for us because the situation is so far from the way my brother is. We never went 24 hours without having a conversation with him."
Tripathi's mother, Judy; father, Akhil; and brother, Ravi, live in the Philadelphia area. The family home where everyone spends breaks and holidays is in Bryn Mawr, said Sangeeta Tripathi, a 2004 Brown graduate who works in global health care in New York.
Judy Tripathi has a private health-care practice. Her husband is CEO of a software company. Ravi Akhil, a 2009 Brown graduate, is a medical student at Temple.
Sangeeta said she last spoke to Sunil several weeks ago before leaving for a work trip out of the country. She returned March 16 and texted her brother but didn't get a response.
Tripathi is 6 feet tall and was last seen wearing blue jeans, a black ski jacket, glasses, and a Philadelphia Eagles beanie. He left his cellphone, wallet, and credit cards at his apartment.
Family, friends, and strangers have been putting up photos, checking homeless shelters and YMCAs, tracing possible paths he may have walked, and combing neighborhoods. The university has "gone above and beyond" in the search, his sister said.
The Facebook page received more than 200,000 hits in the last 48 hours, Sangeeta Tripathi said.
"There's been a really incredible response in the Philadelphia area - from people we know and don't know."
Contact Susan Snyder at 215-854-4693, firstname.lastname@example.org, or follow on Twitter @ssnyderinq. Read her blog at http://www.philly.com/philly/blogs/campus_inq .