Four males and three females are in custody having been arrested on suspicion of various offences.
Police were called at approximately 16:16hrs on Thursday, 10 June to Prentis Road, SW16 to reports of stabbing.
Officers and the London Ambulance Service (LAS) attended the scene and found a male with a stab wound to the chest.
He was taken to a hospital in central London where he was pronounced dead at 16:51hrs.
Police believe they know the identity of the victim, who is in his late teens, and have informed next of kin.
Formal identification and a post-mortem examination will follow in due course.
Police remain on scene and there are currently road closures along Prentis Road. The public are advised to avoid the area.
The investigation is in its very early stages and work to establish the circumstances continues.
Anyone with any information is asked to call police on 101 quoting CAD 5897/10JUNE.