The fatally injured teenager was found by ambulance staff after emergency services were called to the Lupus Street area following reports that a youth had been stabbed. He was taken to a south London hospital where he died a few hours later.
A spokesman for the Metropolitan Police said: "A murder inquiry is now under way and an incident room will open in due course under detectives from the Specialist Crime and Operations Directorate. We must retain an open mind re the circumstances of the incident and any motive at this early stage."
The victim's mother, Pauline Hickey, who lives 100 yards from the murder scene, did not want to comment but an unidentified man at the family home said: "She's broken hearted."
Evgeny Onegin, 22, whose third storey flat overlooks the crime scene said his flatmate saw the boy's attackers flee. He said: "My flatmate saw him bleeding out. He said he could see the wound bleeding out from all the way up here.
"He saw three or four guys running off up the street. Lots of people gathered quickly. The victim was shouting and people called an ambulance as they realised what happened."