The teenager found stabbed to death in the stairwell of a Wandsworth block of flats has been named.
Peter Hagan, 16, was found with multiple stab wounds in Albion House, Neville Gill Close, at about 1.30am on Sunday.
The teenage victim, who was found dead at the scene, is understood to have attended a house party in Albion House.
The murder scene is next to King George's Park.
A murder investigation has been launched and police are urging anyone at the party to come forward and speak to police.
Detective Chief Inspector Nick Scola, of the Homicide & Serious Crime Command said: "I believe the victim had attended a party in Albion House.
"I need to trace everyone at that party, and in particular I am appealing for any information about a group of between five and eight males seen running from the scene into the surrounding streets and possibly through King George's Park."
Nine people have been arrested in connection with the incident and eight have been bailed pending further enquiries.
However, one person remains in police custody.
A police spokesman said: "Although we await formal identification, we are satisfied the victim was Peter Hagan.
"A post-mortem examination was scheduled for Sunday, February 17 and will recommence later today (Monday, February 18)."
Any witnesses or anyone with information should call 020 8721 4005. To remain anonymous call Crimestoppers on 0800 555 111.
Did you know Peter Hagan? Leave your tributes by calling the newsdesk on 020 8722 6343.