It happened Monday around 4:30 p.m. in the area near Somerset Drive and Coliseum Street.
According to the Los Angeles Police Department, the suspect followed the victim from the MTA station at Crenshaw/Expo and tackled her into the bushes before sexually assaulting her.
A bicyclist passing by heard the victim's cries for help and called police.
The suspect ran away from the scene and was last seen headed northbound on Somerset Drive.
The suspect is described as a man between 20 and 30 years old, about 6'2" tall, and weighing between 180 and 200 pounds. He was wearing a black beanie, t-shirt, black shorts, white socks, and black shoes. He was also carrying a gray backpack.
Anyone with information is asked to contact Southwest Detectives at 323-290-2976 or 877-LAPD-24-7.