Officers attempted to stop the van in which he was travelling before it ploughed into vehicles in Du Cain Road, Shepherd’s Bush on Monday night.
The boy, in his late teens, ran off but was killed by a Central Line train near East Acton station after he fled.
The Independent Office for Police Conduct (IOPC) is investigating the incident, which happened just after 8.30pm.
The police vehicle was not pursing the van at the time it collided with other cars and officers were not giving chase on foot, Scotland Yard said.
Chief Superintendent Lou Puddefoot, in charge of policing in Central West BCU, said: “I am extremely sad to confirm the death of this teenager, and my thoughts and condolences are with his friends and family following this tragedy.
“We are in contact with his family, offering specialist support and updates on our work to determine what happened.
“This has caused devastation to the young man’s loved ones, and we also understand how concerning an incident like this is for local people.
“Since the initial incident, representatives from our Professional Standards Department have visited the scene and are continuing to gather evidence.
“The case was referred to the Independent Office for Police Conduct (IOPC) and after a thorough assessment, the IOPC has confirmed that is now for the Met to review, and to find out whether anything could, or should, have been done differently.”
Witness Mike Hill told the Standard: “There was the police helicopter with a spotlight on the train tracks. There were so many police and ambulances, so many I couldn’t count them.”
A post mortem and formal identification will take place in due course. There have no arrests.
A member of the public, who was in one of the cars hit by the van, was taken to hospital as a precaution.
Anyone with information is asked to call police on 101.