Arlington Heights police said the alleged assault happened on the top level of the Eastman Parking Garage at 155 East Eastman Street around 3:30 p.m.
The suspect allegedly approached the teen and asked for help with an issue involving his vehicle. The teen got into the suspect's vehicle, where he assaulted her, police said.
The victim and her guardian reported the alleged assault to police early Saturday evening. She was taken to a local hospital for a medical evaluation.
Police said the suspect is about 6 feet tall and weighs 200-250 pounds. He has dark hair and wore black t-shirt and black athletic shorts.
The suspect's vehicle is described as an older model gray sport utility vehicle.
Police asked anyone with information to call them at 847-368-5300.
Further information was not immediately available.