Detectives are appealing to trace a man they want to speak to in connection with the murder of Khalid Safi in Acton last December.
Khalid, 18, living in Southwark at the time of his death, was found suffering stab injuries after an altercation in Victoria Road, W3 at about 18:30hrs on 1 December 2016.
He was taken by the London Ambulance Service to a west London hospital where he died a short time later.
A post-mortem examination on Friday, 2 December at Uxbridge Mortuary gave cause of death as a stab wound to the heart.
Officers have now released a picture of a man they want to talk to about the events of that night - he is 19-year-old Raza Khan. Police are urging anyone who recognizes him or knows where he is to contact police immediately.
Detectives believe Khan is likely to still be in the UK. He is known to have links to some London areas, including Acton, Wembley, Ilford, Friern Barnet and Tottenham and also to Dover, in Kent.
Detective Chief Inspector Sam Price, who is leading the investigation for the Homicide and Major Crime Command, said: "We are continuing our appeal for information about this fatal stabbing. We believe that some witnesses to the fatal stabbing or the moments leading up to it have not yet come forward and we would urge them to make contact with police as soon as possible.
"We are particularly keen to trace Raza Khan who we believe has crucial information about what happened to Khalid."
Anyone with information is asked to call the police incident room on 020 8721 4054. To give information anonymously contact Crimestoppers on 0800 555 111 or visit www.crimestoppers-uk.org
Two people arrested in connection with this murder.
A 19-year-old woman [A] arrested on Wednesday, 7 December 2016, and released on bail, was charged on Wednesday, 16 August with conspiracy to commit GBH.
A 22-year-old man [B] who was arrested on 29 March on suspicion of assisting an offender has been released with no action.