A 15-year-old boy was robbed of his mobile phone while walking in Northampton on Saturday, December 17.
Northamptonshire Police are appealing for witnesses following the incident at about 8.50pm.
A spokesman said: “A 15-year-old boy was walking towards Weston Favell along the footpath parallel with Lumbertubs Way when he was assaulted by three teenage boys who made off with his iPhone 5.
“The victim suffered bruising to his face, shoulder and head and a swollen lip.
“The offenders were all white and aged about 15. The first was around 5ft 8in with a slim build and short brown hair. He was wearing a black Adidas tracksuit with white stripes. The second was about 5ft 9in and wore a grey, waist-length zip-up jacket and was carrying an Adidas bag. The third was around 5ft 7in with a slim build and was wearing a black Adidas tracksuit with white stripes,” he added.
Witnesses or anyone with information can contact police on 101 or Crimestoppers anonymously on 0800 111 555.