The attack took place in Adelaide Close on the Moorlands Estate.
Scotland Yard said the victim was with his friend on the way to the friend's relative's house in Brixton when the attack happened.
The suspects were described as two young black men.
More top news
If you are black and a Londoner new figures reveal you are three times more likely to be Tasered by police.
Cloudy with scattered showers for the rest of the week.
Figures show an increasing trend for barriers to be left open, potentially making life easy for fare dodgers.