Three teenagers believed their lives were in danger when a stranger came at them with a knife near to a school.
A 16-year-old girl and two boys aged 15 were sat in a play area in Emerson Valley when they were threatened on Friday evening.
They managed to escape unharmed, say police.
The offender had opened his jacket to reveal a kitchen knife to the teens while at the top of Oaken Head backing on to Emerson Valley School.
Police would like to speak to in connection with the incident, which happened at around 9.10pm.
The offender is white, aged approximately 17 or 18, slim, around 6ft, with a pale complexion and goatee beard. He was wearing skinny jeans pulled down slightly and a bomber jacket with a black hoodie underneath with the hood pulled up.
PC Samantha Pearce said: “The victims in this case suffered a nasty experience and thought their lives were in danger.
“Clearly this behaviour is not tolerated in Milton Keynes and we would appeal who saw what happened, or thinks they may know the offender from the description provided, toplease contact the Thames Valley Police Enquiry Centre on 101.
“If you don’t want to speak directly to police, contact Crimestoppers anonymously on 0800 555 111.
“No personal details are taken, information is not traced or recorded and you will not go to court.”