Teenagers were robbed by a man brandishing a knife on the underpass of Westcroft roundabout in Milton Keynes.
The two 17-year-old boys handed over their phones, a black Nokia Lumia 620 in a red and black case and a black iPhone 4S, after the man threatened them as they walked home.
They were then asked for money, but didn’t have any so the offender ran off - first towards the Redway then changed direction towards Tattenhoe.
It happened between 9pm and 10pm on Monday.
The offender is a white man, 5ft 8ins to 6ft tall, with a skinny build, late teens to early twenties. He wore a black hooded top, with the hood up and his face was covered by a black scarf with white spots on it. He also wore black tracksuit bottoms.
If you saw anyone acting suspicious in the area or have any information about this incident contact Det Con Susan Russell on 101.
If you don’t want to speak directly to the police, you can 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.