Xavier Pinero, 20, of 44 Helmig St., was arrested by Fourth Squad detectives Wednesday.
Police said Pinero was one of three men who displayed a handgun and demanded cash and the cell phones of three teens on a wooded path near Route 111 and Woodhollow Road on Tuesday at about 1:15 p.m.
A short time later, the same men stole an iPod from two teens who were skateboarding on Ledgewood Drive in Smithtown, police said. One of the teens also was assaulted, police said.
Pinero has been charged with two counts of robbery and was scheduled for arraignment Friday in First District Court in Central Islip.
Police are still looking for the two other men involved in the robberies. Those with information can call the Fourth Squad, 631-854-8452, or Crime Stoppers, 800-220-8477.