The robbery was reported at about 9:40 p.m. in the 1500 block of 15th Street.
The 19-year-old victim was walking when she was approached by two other women, who pepper-sprayed her, punched her and took her jacket, according to police.
The suspects, believed to be in their mid-20s, ran away and had not been found as of this morning.
The victim was taken to San Francisco General Hospital to be treated for her injuries, police said.
Anyone with information about the robbery is encouraged to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.