A pervert impersonated a cop as a guise to sexually assault a teen boy in Brooklyn, police said.

The 15-year-old had thrown a bag of chips onto the platform of the 53rd street subway station in Sunset Park when the sicko approached the teen.

He was dressed in civilian clothes but displayed what appeared to be a police shield and ordered the frightened teen to come with him to a nearby white van around 9:30 a.m. Friday, cops said.

The creep drove the boy to 92nd Street, near Dahlgren Place in Bay Ridge, and sexually assaulted the victim, cops said.

He then drove back to 38th Street, where he let the teen go.

Cops said the suspect stands about 5’8” tall and weighs approximately 145 pounds. He has a bald head, gray mustache, and a mole under the left side of his lip.