The victim, who is from the Clacton area, has not yet been named by police.
However, tributes began flooding onto the social networking site Twitter using the hashtag #RIPJay.
One Twitter user, under the name Mary-Ellen1, said:
RIP Jay my little brother, taken too young. We will get you justice.
RIPJay, the mark you left on this Earth is irreplaceable, the mark you left in our hearts is unforgettable.
More top news
The teenager's family spoke of their "torment and pain" after serial killer Levi Bellfield finally confessed to her murder.
The fatal collision happened in Hackney, east London, just before midday on Tuesday.
Police are hunting three youths in connection with the incident which happened on January 4 in Romford.