Ilyas Habibi was found injured in Sutton High Street just before 7.10pm on December 5.
Officers, London Ambulance Service crews and an air ambulance were called to the scene.
On arrival, Ilyas was found suffering from knife injuries, and he was provided with first aid.
He was pronounced dead at the scene just before 7.55pm.
It was found by police that Ilyas arrived at Sutton High Street by train and minutes after he came out of the station he was involved in an altercation with the suspect who then fled the scene.
Officers say that it “isn’t clear if the suspect was also injured” and are asking the individual, or anyone who knows them, to come forward.
Ilyas’ family have since been notified and they are being supported by specialist officers.
They ask that their privacy be respected at this time.
Tributes have since been paid to Ilyas with flowers and lit candles left at the scene of the incident.
Several candles outlining Ilyas’ name are also among the tributes at the scene.
A crime scene on the High Street and near the train station was closed today after forensics being on scene for two days.
Detective Chief Inspector Mike Nolan who leads the investigation said: “We know that Ilyas arrived at Sutton High Street by train.
“Minutes after he came out of the station he was involved in an altercation with the suspect who then fled the scene.
“Ilyas had suffered fatal wounds. It isn’t clear if the suspect was also injured. If you know the suspect, or if you are him, please get in touch.
“Members of the public who have information and material they want to share with us can do so via our online web portal.”
Chief Superintendent Andy Brittan, leading policing for the Met’s South Area Command said: “I know that those who live and work in Sutton will be shocked and saddened at the loss of a young life on the streets that they call home.
“I share those emotions and would like to reassure local people that we are doing everything we can to support our homicide colleagues in identifying and apprehending the person, or persons responsible.
“I urge anyone who is concerned to approach officers on patrol and speak with them or get in touch with their Neighbourhood policing team.
“Our thoughts are with the victim’s family at this sad time.
“I would like to thank the community for their patience as we carry out our enquiries, and urge anyone with information concerning this incident to get in touch.”
Anyone with information concerning this incident should call the incident room direct on 0208 721 4622; call police on 101 or Tweet on ‘X’ @MetCC quoting 6107/5DEC.
To remain 100% anonymous call the independent charity Crimestoppers on 0800 555 111 or visit crimestoppers-uk.org.