The attack happened in the 6300-block of South Paulina Avenue, according to authorities.
The girl was walking down the block around 10:15 a.m. when an unknown offender approached her, pulled her into a gangway and sexually assaulted her at gunpoint, police said.
The offender took her cell phone, iPod and fled the scene, officials said. The girl is in stable condition at Comer Children's Hospital.
The suspect is described as a male, black, 16-18 years of age, 5'5 to 5'8, 140-160 pounds with short hair and a light complexion, police said.