He remains in custody at a south London police station after being arrested on suspicion of murder.
Police were called at 4,45pm on Tuesday, 12 October to reports of a stabbing on a playing field in Craneford Way, Twickenham.
Officers attended along with London Ambulance Service and found an 18-year-old man with stab injuries.
He was taken to hospital but was pronounced dead at 5.45pm He has since been named as Hazrat Wali, from Notting Hill.
His family continue to be supported by specially trained officers.
A post-mortem examination has been scheduled to take place at Kingston Mortuary on Friday, 15 October.
Anyone who has information or footage of the incident is asked to call police on 101 or tweet @MetCC quoting 5697/12OCT. You can also upload evidence here.
Information can also be provided to Crimestoppers, anonymously, by calling 0800 555 111.