Fola Orebiyi, 16, was knifed in the neck and back following a "trivial" argument in the streets of Notting Hill on July 3 last year.
The 15-year-old who wielded the knife was today found guilty at the Old Bailey of murder following a trial.
He remained emotionless as he was remanded in custody to be sentenced on February 10.
A 17-year-old boy who was accused of involvement in the killing broke down and sobbed as he was cleared by the jury.
Prosecutor Tim Cray told the court Fola lived close to the Portobello Road area where he was killed.
"The cause of the trouble that led to the stabbing seems to have been trivial, compared to the harm that came from it", he said.
In the weeks before the murder, one of Fola's friends had a fight with the 15-year-old killer, trading insults.