Halifax Regional Police are investigating a robbery that left a 21-year-old man with a cut on his hand.

Police were called to the area of Thomas Raddall Drive and Lacewood Drive in Clayton Park at 10:30 Thursday night. They say the victim was assaulted with a knife and robbed while selling a mobile phone.

The alleged attacker contacted the victim via social media to make the purchase, say police.

Paramedics treated the 21-year-old man at the scene for the cut on his hand and he was released.

While looking for the attacker, police say they found several stolen phones.

They're still investigating.