At around 9.45pm on Wednesday, May 29, a man walking into Northampton along Barrack Road was approached by three unknown men close to the pedestrianised junction with Ash Street.
The three men asked the victim for cash, before grabbing his mobile phone and threatening him.
All three are described as white men aged in their 30s to 40s. All wore dirty tracksuits and spoke with English accents.
One was described as having cropped brown hair, another as tall and slender, with spiky blonde hair. The three men are thought to regularly visit the Barrack Road area.
Anyone who saw the incident, or has information about it, should call Northamptonshire Police on 101, or Crimestoppers in confidence on 0800 555111.