Suspected gang members were arrested in raids in a "robust" police response to a spate of stabbings.
Eight south London addresses were targeted in relation to street attacks, including the murder of Kwame Ofosu-Asare, 17.
Four young men are being questioned for conspiracy to commit grievous bodily harm unrelated to the death of Mr Ofosu-Asare in Brixton.
Chief Superintendent Matt Bell said: "Lambeth 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."Reuse content