Police are trying to trace two youths who fled from officers along with a teenager who later died on a motorway.
Wasid Ali died when he tried to cross the motorway on foot
As the officers approached the youths, they ran off and one scaled a fence onto the M1.
Wasid Ali, 13, died on Tuesday just after 1915 GMT on Tuesday after being hit by a car on the motorway.
The Independent Police Complaints Commission (IPCC) has been informed of the death and an inquiry has been launched by the Metropolitan Police.
The silver Seat saloon which hit the teenager on the northbound carriageway, was then hit by a dark-coloured BMW.
The two male drivers were injured and taken to hospital. One suffered a head injury and the other an injury to the chest.
The officers were investigating reports of youths pushing a suspected stolen moped in an underpass in Kingsbury, north-west London, when the pursuit began.
Wasid Ali's aunt Rashda told BBC London: "If anyone saw them that day please come forward and help.
"Call the police because the whole family is distraught."
Police have appealed for witnesses to the incident to contact them.