The incident happened around 6:15 a.m. on Jan. 9. Police said a man approached a female rider on a bus on Pico and La Cienega boulevards.
The suspect struck the victim twice on the face and took her cellphone. He got off the bus when it came to a stop.
The victim was treated for minor injuries.
Anyone with information was asked to call police at (877) LAPD-24-7.