The youths struck as the boy stood outside the Sheen Lane Centre at 8.30pm on Saturday.
They threatened to smash a glass bottle over his head unless he handed over his bike. He refused and the boys left empty handed.
Both youths are 17 years old. The first is white, 5ft 5ins, wearing a white baseball cap, white jacket and black trousers.
His accomplice is black, 6ft tall, wearing a black jacket, pink shirt and tracksuit bottoms.
Ring 020 8247 5842.
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