A 16-year-old boy was threatened with a knife during an attempted robbery in Rotherham Avenue, Luton.
The incident happened as the victim was walking near the junction of Farley Farm Road on June 5 at around 4pm.
He was approached by three men who demanded he empty his pockets, and when he refused, one of the offenders produced a knife and threatened him.
The other offender then searched the victim but found nothing of value and the three men made off towards Tinsley.
All three offenders were black males aged 19 or 20 years old.
The one who was armed with the knife was around 6ft 2, of stocky build, wearing a black hooded top, light blue jeans, trainers and carrying a black side bag.
The other two were both around 5ft 8 and of average build.
Call Det Con Rebecca Kitts in confidence on 01582 394442 or 101.