It happened at 1:10 a.m. on Centerwood Street.
The 18-year-old girl left a party with friends on Parkway Boulevard in Wyandanch.
They were walking down the street when a fight broke out nearby between two groups of men.
During the fight, shots were fired, and one of the bullets grazed the girl on her upper body.
She was taken to Good Samaritan Hospital Medical Center in West Islip where she was treated and released.
The suspect is described as a black man with a dark complexion, between 19 and 20 years old, 5 feet 10 inches tall and 160 to 170 pounds.
Detectives are asking anyone with information on this incident to call the First Squad at 631-854-8152 or anonymously to Crime Stoppers at 1-800-220-TIPS.
All calls will be kept confidential.