Dogan Ismail, from Peckham, was attacked outside Latimer House in Walworth, on Sunday afternoon, and died at the scene.
Police said Dogan was stabbed when he and and his brother were involved in a row with up to four males.
A 15-year-old boy has been arrested on suspicion of murder and a woman, 39, is also being questioned.
A post-mortem examination was due to be held at Greenwich mortuary on Monday. His next of kin have been informed.
Investigating officer, DCI Matt Bonner, said: "I appeal to anyone who knows of his whereabouts, or has any information that could assist us, to come forward.
Anyone with information is asked to contact the incident room on 020 8358 0200 or Crimestoppers anonymously on 0800 555 111.
A 15-year-old boy and a 39-year-old woman arrested on Sunday in connection with the incident were bailed yesterday to return pending further inquiries.