He died in hospital following the stabbing which police said happened after "an altercation between two small groups of young males".
No arrests have been made as part of the murder investigation.
Det Ch Insp John Massey said he "didn't believe" anyone involved had travelled on the Tube.
"There were a large number of people present when emergency services arrived at the scene," he said.
"Although many have come forward, I want to ensure that we have spoken to all potential witnesses," John said.
Floral tributes have now been left near to the spot where Malcolm was stabbed.
Malcolm, a student at a college in Clapham, became the second teenager to be stabbed to death in south London within 24 hours.
Jay Hughes, 15, died on Thursday night after being stabbed in a chicken shop in Randlesdown Road, Bellingham. No arrests have been made in that murder investigation as well.