Sylvester Akapalara, 17, of Streatham, was shot dead in a stairwell on the Pelican Estate in Peckham on Wednesday.
Sodiq Adeojo, 18, and a 17-year-old male have been charged with the killing. They are due at Camberwell Green Magistrates' Court on 3 January.
Sylvester, a Sierra Leonian national, was said to be in the top 30 in the country for 400m running.
Steve Bosley, of athletics club the Herne Hill Harriers, said he was "quiet and unassuming".
More than 760 people have joined a Facebook group set up in memory of the teenager, who was also known as Sylvester Da Donappa.
He was found bleeding to death on the fourth floor of Heron House on the Pelican Estate and had been shot in the neck and chest.