Authorities say the suspect has struck at least five times in the past eight days.
In each incident, the suspect enters the commercial establishment, simulates a firearm inside a black plastic bag and demands cash.
The first four incidents were last week, while the latest occurred Tuesday morning inside a grocery store at Broadway and 103rd Street.
No injuries were reported in any of the incidents, which took place at the Metro PCS on Woodside Avenue, the Nagle Bakery on Nagle Avenue, OK Market on Madison Avenue, Pasticceria Amore on 71st Road and Convenience Grocery on Broadway.
Anyone with information regarding these incidents is asked to call Crime Stoppers at 1-800-577-TIPS (8477).