Police did not provide the age of the victim, who was taken to Good Samaritan Medical Center in West Islip where he is listed in critical condition.
Police responded to a call for a pedestrian struck by a vehicle at 10:26 p.m. and found the teen lying unconscious on Udall Road.
Witnesses at the scene reported seeing a light-blue car traveling north on Udall Road and turning west on Alinda Avenue.
The blue car is believed to have damage to both the driver's side headlight assembly and the driver's side-view mirror, police said.
Anyone with information can call Crime Stoppers at 800-220-8477 or the Third Squad at 631-854-8352. All calls will be kept confidential.