Sell's friends know a lot about search and rescue. They spent the afternoon setting up a command post in the city and making a plan to systematically turn over every stone until they find him. Finding a missing person is nothing new to these men. They've all done this before in the armed forces, and as volunteers in the wake of disasters like Superstorm Sandy.
Sell, 30, goes by Will. He was in San Francisco visiting friends for the holidays. He's a Navy veteran who attends college in Portland, Oregon, but travels all over, volunteering with returning veterans and disaster survivors.
"Will is a man who would give anything to you even if he didn't have it," Sell's father Dennis Newman said."He worked out on the East Coast with Sandy, he worked the tornadoes in Illinois in April and May and worked the Moore, Oklahoma tornado in May."
Newman says he's worried that all that giving to folks who've been through so much has taken an emotional toll on his son. Friends say he hadn't been acting like himself lately. On Dec. 15, the searchers say friends became concerned enough to bring Sell to San Francisco General Hospital, where he stayed for two days. Once doctors determined it was OK to release him, friends say he apparently checked out of the hospital and disappeared.
"We're checking the shelters, the areas that we assume he may be at," David Casler said.
They're putting up fliers around the city, describing will as six feet tall and 200 pounds, likely with long hair and a beard. Anyone who sees him should call the police, though they stress Sell is not in any kind of trouble.
"He's a great friend and I want him home safe," Jeffrey Lemberger said."I will not leave San Francisco until I've basically upheaved it and turned this place upside down looking for him."
And so does Sell's father, who said he hopes his son hears his emotional plea.
"I just want him to know that his family loves him, and that we, nothing else matters except for him to let us know that he's OK," Newman said.
If you think you saw Sell, know his whereabouts or want to help search for him you're encouraged to call the San Francisco Police Department at 415-315-2400 or 775-557-8459.