In each case, investigators say the man approaches the victim, displays a weapon and demands property.
Twice he displayed a firearm, and in the other robbery he was brandishing a knife.
The victims have been two 17-year olds and a 15-year old, with two of the robberies occurring in the same building on Seaview Avenue.
Police have released a surveillance photo of the man they are looking for.
Anyone with information is asked to call Crime stoppers at 1-800-577-TIPS (8477).
The public can also submit their tips by logging onto the Crime stoppers website at http://WWW.NYPDCRIMESTOPPERS.COM or by texting their tips to 274637 (CRIMES) then enter TIP577.