The incident happened just after 3 a.m. Saturday in Patchogue.
Authorities say the man in the picture dragged a 24-year-old woman away from Main Street and into a grassy area, where he beat, sexually assaulted and robbed her before fleeing the scene.
The victim suffered a broken nose, cuts and bruises.
She was treated and released at a local hospital.
Fifth Squad detectives believe Main Street was crowded Friday night into Saturday morning, and numerous people may have encountered the suspect before or after the attack.
The suspect is described as a tall light-skinned Hispanic or black male, with a thin build in his 20s. He was wearing a black T-shirt, dark colored jeans and a wool ski type hat.
Detectives are asking anyone with information on this case to call Crime Stoppers at 1-800-220-TIPS.