The woman was walking home with a friend on Sheffield Avenue just north of Fullerton at about 1:45 a.m. when police said an unknown man approached her from behind. The man touched her inappropriately and then fled northbound on foot, police said.
The suspect is described by police as a man in his mid-20s who is 5'10" tall with black hair and was wearing a gray sweatshirt and black shorts.
Anyone with information is asked to contact Area North detectives at (312) 744-8261.