Tashawn Watt, 19, suffered multiple injuries in Sydenham on Friday night.
The victim’s mother visited the scene minutes later. She is being supported by officers and relatives.
Tashawn was the 18th London teenager to be killed so far this year, including 16 who have died from stab wounds.
The first six months of 2021 has seen the teenage death toll already surpass the total for the whole of last year.
Police said officers and ambulance staff had attempted first aid but Tashawn died at the scene after suffering what witnesses described as a “flurry of blows”.
A relative said his mother was “in pieces” as she met police at a cordon in Miall Walk.
A post-mortem examination was due to be held at Greenwich Mortuary on Tuesday.
Detective Chief Inspector Chris Wood, leading the Sydenham murder inquiry, said: “My officers have been working 24/7 following a number of leads and enquiries following this senseless loss of life and our investigation is gathering pace.
“I had said previously that support from the community would be crucial and this remains the case. There are people who have spoken to us and told us what they know and I am very grateful to them.
“The work we do can’t be done alone - support and information from the public is always invaluable in removing violent offenders from our streets.”
Scotland Yard has now launched 61 murder investigations this year.
Tashawn was killed during another weekend of bloodshed in London.
Jason Nyarko, 26, from Lewisham, was fatally stabbed at an illegal rave near Millwall Football Club’s ground in South Bermondsey.
Police found Mr Nyarko at an industrial unit in Stockholm Road, where the event was still taking place, shortly before midnight.
A 16-year-old boy was taken to hospital with head injuries and arrested in connection with the incident.
Detectives warned earlier this month that the capital was on track for its worst ever year for teenage killings as coronavirus restrictions lift further.
Last year, 15 young people died in attacks.
If the rate continues, the number of teenage fatalities for the year will top 30 for the first time, surpassing the current peak of 29 in 2008, as well as the 26 recorded in 2019 before the impact of lockdown reduced the death toll last year.