The boy, 16, was walking behind 951 Atlantic Ave. at about 6 p.m. when he was approached by three males, police said in a news release.
The victim tried to run away, police said, when the suspects demanded he turn over his belongings. One of the attackers "pushed the victim, pulled out a knife and demanded the victim's cellular telephone," police said.
The victim, who was not injured, handed over his phone and the three robbers ran away, headed north, police said.
The knife-wielding suspect is described as about 5-foot-8, with a slim build and short hair, wearing a blue Yankees baseball cap.