Police are warning commuters to be cautious of their belongings when on crowded buses and trains.
The crowded conditions are ideal for thieves, police said.
Video released by police show a man taking a wallet right out of the back pocket from the person standing next to him while on a crowded Muni bus.
The victim, Abe Mirrashidi of San Francisco, said he did not feel a thing.
Mirrashidi said he was riding Muni with two kids at the time of the theft.
"I was a sitting duck," he said. "No one wants to be the mark."
By the time he realized his wallet was gone the thief had used his credit cards. Mirrashidi is no longer carrying anything more than bus fare on the bus.
Police are urging commuters to keep personal items where they can see and feel it.
"Keep personal items like wallets or purses in front of you or in your front pocket," San Francisco Police Officer Carlos Manfredi said.
Police describe the wallet thief as a male standing about 6 feet 2 inches tall and has a gold front tooth. Officer said they would like to make an arrest before he strikes again.