Police were called at 5.40am today, Friday, to reports of a stabbing in an alley behind Breezers Bar on West End Road.
Three men, two wearing dark hoodies, approached the victim and his friend and they were attacked.
One of the men used some sort of weapon and stabbed the 17-year-old victim under his chin, causing injuries to his jaw and mouth.
The three men ran off from the scene.
The victim walked to a nearby property and called for an ambulance.
He has had stitches and will require some dental work, said police.
Anyone with information should contact police on 101, quoting crime reference WB1704313.