Suspected gang members were arrested in raids today as police made a "robust" response to a spate of stabbings.
Eight south London addresses were targeted in relation to street attacks, including the murder of 17-year-old Kwame Ofosu-Asare.
Four male youths are being questioned for conspiracy to commit grievous bodily harm unrelated to the death of Kwame, in Brixton, the force said.
Chief Superintendent Matt Bell said: "Lambeth borough is committed to reducing serious youth violence and gang activity and we felt it vital that we take robust and prompt action in order to pre-empt any potential future violence."
Teenager Kwame was discovered on early Friday evening with stab wounds in Adelaide Close, Moorlands Estate, Brixton.
He and a friend were chased by two knifemen, police said.
Officers were investigating if the killing is linked to another stabbing on Friday when a 17-year-old boy was attacked outside Norwood bus garage, Ernest Avenue, West Norwood at around 1.15pm.
There were also a number of gang-related street attacks in Lambeth on February 25, the force said.
The dawn raids were carried out across Lambeth where six other attacks took place.
Mr Bell said: "I want to reassure the community and the wider public that detectives are working around the clock to gather evidence and find those responsible, whilst extra patrols have been stepped up in the borough to act as a strong deterrent to anyone thinking of committing further violence in the aftermath of these incidents."
Commander Steve Rodhouse added: "Today's raids send out a clear message that the mindless violence that has affected Lambeth and other parts of London recently will not be tolerated.
"Our priority is to find out what has happened, bring those responsible to justice and prevent any further incidents in the coming days and weeks. We will continue to aggressively pursue any lawful opportunities against those who choose to become involved in violent crime, so that we can protect potential future victims, the community and the wider public."
Kwame, who lived in Catford, south-east London, was en route to hospital when he died in the ambulance.
It is believed Kwame, a sixth form student, and his friend were on their way to the friend's relative's house when they were chased by two young men and assaulted. Kwame's friend was not injured.
Anyone with information should call the incident room on 020 8721 4205; if you wish to remain anonymous call Crimestoppers on 0800 555 111.