Jordan Wright, 19, was stabbed to death in Blackheath on 19 April 2017.
Police and paramedics were called to Hervey Road at the junction of Begbie Road at around 8.10pm.
Mr Wright, from Catford, was found suffering from stab injuries and died after being taken to hospital.
Detectives from the Homicide and Major Crime Command are appealing for witnesses and information.
The officer leading the investigation, Detective Chief Inspector Diane Tudway, said: "I believe Jordan was part of a group of young men who had entered the park together before he was stabbed.
"Those other young men will know who they are, and I urge each of them to call police or Crimestoppers and simply describe what they saw."
Anyone with information is asked to call the incident room on 020 8721 4005 or via 101.
To remain anonymous, contact Crimestoppers on 0800 555 111 or via the crimestoppers-uk.org website.