The 34-year-old out-of-state tourist had been walking in the 100 block of Gateway Boulevard around 10 p.m. when he was assaulted by four to six men, police said.
The suspects knocked the man, of Southlake, Texas, to the ground and stole his money. As he lay on the ground, one of the men produced a silver pocket knife, which he used to cut a clump of hair from the victim's head, police said.
The suspects, who are described as men in their early 30s who wore dark clothing, fled on foot.
Anyone with information is asked to contact South San Francisco police at (650) 877-8900.