Police were called at approximately 17:34hrs on Saturday, 6 March to reports of a fight in Edington Road, Abbey Wood.
Officers attended along with the London Ambulance Service and found an 18-year-old man with a stab injury to his chest. He was pronounced dead at the scene.
His next of kin has been informed and are being supported by specialist officers. Formal identification is yet to take place.
Officers from the Met’s Specialist Crime Command are carrying out enquiries and a crime scene remains in place.
Detective Sergeant Michael Hartley said: “A young man has lost his life in the most tragic circumstances and officers will work round the clock to bring those responsible to justice.
“We are still in the early stages of the investigation and I would ask anybody who was in the area yesterday evening – or who has information about the attack – to contact us immediately.”
There have been no arrests.
Anybody with information or footage that could help the investigation is asked to tweet @MetCC or call 101, quoting CAD 5771/06Mar. To remain anonymous contact Crimestoppers on 0800 555 111.