A man pulled a knife on three youngsters as they were walking in Kettering.
A 17-year-old boy and another boy and girl were walking along the side of the tennis courts in North Park, Kettering, when they were approached by a man who asked for directions.
He then pulled out a knife and demanded money.
The three ran along Lobelia Road and Cedar Road and were not aware of being chased by the offender.
The offender was a white man of slim to medium build, between 5ft 6in and 5ft 10in and about 20-years-old.
He wore a black Nike hooded sweatshirt with a white logo on the chest and had an Irish accent.
Witnesses to this incident, or anyone with information about it, can call Northamptonshire Police on 101 or information can be given anonymously to Crimestoppers on 0800 555111.