Police said the victim was hospitalized with an undisclosed number of stab wounds after the attack, which took place near Catherine Avenue at about 1:30 p.m.
His condition was not known Wednesday.
Police said the victim and a friend were driving along Hempstead Turnpike when the victim asked his friend to stop the car so he could buy cigarettes at a local deli.
As he walked toward the deli, police said, the victim got into some sort of verbal dispute with the suspects, whom he didn't know -- and police said the trio pulled the victim's hoodie over his head, began punching and stabbing him, then stole his designer watch.
The victim did not realize he had been stabbed until he got back into the car, police said.
Detectives are seeking the three suspects, and police are asking anyone with information about the attack to contact Crime Stoppers at 800-244-TIPS. All calls will remain confidential, police said.