Police said the victim, 16, was walking near Centennial Park on Centennial Avenue about 8 p.m. when he was approached by the two men wearing masks.
One man demanded money, and when the victim said he did not have any, both men pushed him against a fence and went through his pockets, police said.
One of the men pulled a knife and slashed at the victim's wrist, cutting him, police said.
Both men then left without getting any proceeds, running south on Babylon Turnpike, police said.
The victim refused medical attention at the scene, police said.
Anyone with information can call Crime Stoppers, 800-244-8477. All calls will be kept confidential.