The incidents happened in the South Shore and South Chicago neighborhoods. One happened in the 8700-block of South Harper last Friday.
The victim, Damien Dyer, tells ABC7 the offender identified himself as a Chicago police officer and told him to get into the car. The cop impersonator then drove him to an alley, pulled out a gun and robbed him.
No one has been hurt in any of the incidents.
Investigators say the offender calls himself "Officer Franklin."