Detectives believe that the men targeted Kwame Ofosu-Asare at random in revenge for an earlier gangland stabbing.
The 17-year-old sixth-form student was walking through the Moorlands estate in Brixton with a friend last Friday when he was chased and stabbed to death in a cul-de-sac.
His friend managed to escape by vaulting an 8ft fence but Kwame was stabbed several times. He died in the ambulance on the way to hospital.
Detectives say they are hunting two knifemen who were spotted on the estate and chased the young men.
Today officers hunting the killers said they are urgently trying to trace the driver of silver minicab thought to have driven the murder suspects around as they looked for a victim.
Police think the suspects could have been picked up in Camberwell and driven around for about 20 minutes before the attack. The cab was spotted driving around the Myatts Field estate and Vassal Road area before it parked up on Moorlands Road.
Two men are seen leaving the cab and walking on to the estate at the time of the murder and then returning to the vehicle just “three to four minutes” later. The cab then headed back towards Camberwell.
Det Ch Insp John McFarlane, who is leading the murder inquiry, said he believed at least two suspects were in the cab. “It appears they were hunting rival gang members and this was a random selection of victims,” he said. “These two boys were innocents abroad. The minicab driver may have vital information that could help with this investigation.”
The Met arrested a 22-year-old man in a dawn swoop at an address in the Brixton area this morning.
Officers from the Trident Gangs Command also seized another 10 gang suspects during further raids in south London. Police have carried out a string of raids in recent days as part of a “robust” response to a series of gangland stabbings.
Eight south London addresses were targeted on Tuesday and four people, including two schoolboys aged 14 and 16, were arrested.
Today Kwame’s father Kwaku, a top Ghanaian TV sports reporter, issued a new plea for help from the public to catch the killers of his son.
Earlier this week he hit out at London’s “gangland madness” when
he told the Standard how his son detested gang crime and had never been involved in any trouble.
Detectives are investigating whether the killing is linked to another stabbing on Friday when a 17-year-old boy was attacked outside Norwood bus garage in Ernest Avenue, West Norwood, at about 1.15pm.
There were also a string of other gang-related street attacks in Lambeth on February 25, the force said.