The theft reportedly occurred in the area of Three Oaks at the St. Lawrence Sports and Community Centre (football pitch) around 17:30 yesterday (Tuesday 12 May).
Officers said that, after the alleged robbery, the victim chased the suspects on foot as they fled the scene on a moped.
Pictured: The area in which the robbery reportedly occurred.
Two 16-year-olds were arrested, but have since been released on bail while the investigation continues.
Police are now urging witnesses to get in touch, and particularly want to hear from a man and woman walking their dog in the area at the time.
Anyone with more information should call 612612 or make an anonymous report via the Crimestoppers website.