Robbers stole shoes from their victim's feet after attacking him in Kettering.
A 17-year-old boy was in Valley Walk when he was robbed between 1am and 1.15am on Monday, August 26.
He was approached by a group of males who tripped him up before kicking and punching him while he lay on the froor.
They then stole the Nike Air Force One trainers - which can sell for £100 - from his feet as well as his mobile phone, red baseball cap and black manbag.
A police spokesman said: "The group of males were described as wearing grey/black tracksuits, some with bicycles."
Witnesses or anyone with information should call Northamptonshire Police on 101.