Thames Valley Police is appealing for witnesses following a robbery in Bletchley.
At around 4.30pm on Saturday (23/1) a 14-year-old boy was riding a bicycle along Rydal Way when he was stopped by four teenage boys.
The group told him to hand over his bike and when he refused, one of the group pulled out a knife and threatened him.
The victim was able to cycle away.
No one was injured during the incident and nothing was stolen.
The offender with the knife is described as a very skinny black teenage boy aged between 15-18-years-old and approximately 6ft – 6ft 1in tall. He was wearing a black balaclava and dark coloured clothing.
Investigating officer Detective Constable Susan Russell, based at Milton Keynes police station, said: “I am appealing to anyone who may have any information or footage from CCTV, dashcams or phones to come forward.