The incident happened on Wednesday, December 21. Police released information about the attack today, December 28.
A spokesman for the force said: “The teenager was with a friend at about 2.15pm when they were approached by a group of older boys who shouted at him to give them his bike.
“The victim and his friend tried to run away but one of the other group chased after him, shouted at him and then punched him in the face.
“The offender was black, aged between 15 and 16 and about 5ft 11ins, of slim build and had short hair. He was wearing a grey hooded top, white tee-shirt and black trousers,” he added.
Officers would like to speak to anyone who may have witnessed this incident or who may have any information regarding it.
Witnesses or anyone with information about this incident can contact police on 101 or Crimestoppers anonymously on 0800 111 555.