Police released surveillance pictures of the man. The alleged incident occurred Oct. 9. Police say the suspect was on the train with the woman, and followed her when she got off at the La Cienega/Jefferson Station.
The woman walked about a block before the man sexually assaulted her near National Boulevard and Eastham Drive, according to police.
The suspect is described as a male Hispanic in his mid to late teens, 5 feet 9 inches tall with a slim build. He was last seen in a brown hooded sweatshirt and tan shorts.
Anyone with information is asked to call Culver City police at (310) 253-6202.