It happened at 7:45 a.m. Monday at 8th and Spring Garden Streets.
A woman in her late teens told police she was forced into a gray Ford Crown Victoria sedan at gunpoint, robbed and sexually assaulted, then dropped off in the 5000 block of Whitaker Avenue in the Juniata Park section of Philadelphia.
She is being treated at Episcopal Hospital.
The victim describes her attacker as an African-American man with a thin build, about 25 years old. He was last seen wearing a white shirt, jeans and black sneakers.
Anyone with information on the case is asked to call the Philadelphia Police Special Victims Unit at 215-685-3251.