Sell had been missing since last week and was last seen checking out of San Francisco General Hospital before he vanished.
Sell's father says he got the call from police as he was driving around looking for his son.
"This woud not have happened if you guys had not immediately jumped in," Dennis Newman said. "Becuase he wouldn't ve seen it, he wouldn't've known."
Volunteers met at a vet center on Market Street Friday morning to come up with a plan for their search. They spent the morning strategizing by trying to gather what volunteers they had, where they would be going and hoping more volunteers would show up to help.
They had put up fliers around the city, describing Sell as six feet tall and 200 pounds, likely with long hair and a beard.
The volunteers had planned to search BART stations, Golden Gate Park and even Treasure Island on Friday.
Sell's family and friends still have a lot of questions, but for the time being, they're just happy to know he is safe.