A man was robbed while walking along Brampton Valley Way, near to the Brampton Halt pub, Chapel Brampton.
The 18-year-old was walking along the footpath when the incident happened between 11.30pm on Ma1 and 12.30am on 2 May.
He was approached by a man, who assaulted him before taking his mobile phone and wallet.
The robber was aged between 25 and 35, around 6ft and of medium build. He was wearing a black hooded top, blue jeans and had his face covered.
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 can contact police on 101 or Crimestoppers anonymously on 0800 555 111.