Police have released an e-fit of a man they want to identify following a robbery in Cottingham Road, Corby.
The victim, a 16-year-old boy, was walking along the road when the offender, who was holding a pocket knife, grabbed him from behind and demanded the boy hand over all his money.
The boy handed over £10 and the offender made off in the direction of Benefield shops.
The incident happened between 2.30pm and 3.15pm on Saturday, August 11.
The offender is described as white, fair-skinned, aged 30-40 and about 5ft 7in to 5ft 8in.
He wore a baseball cap and beige jacket.
Witnesses to the incident, or anyone who may be able to identify the man in the e-fit, are asked to call Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555111.