It happened around 10:30 a.m. on Sunday, July 24, in the 8900-block of South Chicago Avenue.
Police have released a sketch of the suspect. Investigators say he pulled his SUV up to a 13-year-old boy and offered him money in exchange for a sexual act.
The boy was able to run away through a nearby park and told an adult what happened.
The suspect is bald and is described as being in his early 30s. He was driving a newer-model, burgundy-colored SUV, possibly a Chevrolet Tahoe.
Police remind residents that children should not be allowed to walk alone.
Anyone with information should call Chicago police.