Evan Flanary, 22, only recently moved to San Francisco, went missing a week ago, and was last seen on June 19 in the Mission District, said his mother, Deborah Berlingeri.
Police are now ‘actively searching’ for Mr Flanary, Officer Wilson Ng, a department spokesman, told the San Francisco Chronicle.
Flanary grew up in Medford, Oregon, where his parents still live. He moved to California four months ago and has been staying with a friend, Berlingeri said. He had just earned his merchant marine union card and was looking for work, she said.
His family launched a website, helpfindevan.com, where they said it is very unlike him to vanish without notice. His phone is no longer in service, and he is said to have no money with him.
Flanary is described as a man with blond hair and blue eyes, standing at 6 feet 1 inch tall and weighing 160lbs.
He was last seen wearing blue jeans, a grey hooded sweatshirt and a UC Berkeley baseball cap, and carrying a backpack.
Police would not specify which app Flanary was using at the time, but there has been an explosion of social networking and dating apps in recent years, from the gay-oriented Grindr to Skout, Banjo and Sonar.
The San Francisco-based Skout, which bills itself as a location-based flirting site, has come under fire recently following reports that three teenagers were sexually assaulted by people they met through the app, reported the Daily Mail.