She was first snatched from the street, before being marched to a nearby flat in King Edward's Road, Hackney, East London.
A 16-year-old attacker ordered she should be put through the sexual ordeal as punishment for allegedly insulting the leader's girlfriend, Snaresbrook Crown Court heard.
The terrified victim was then led to another address on the Frampton Park Estate, where the nine lads forced themselves on her.
One of them told the terrified victim, now aged 16: 'I can't help you now, I'm with my boys.'
Following a six-week trial, six of the youngsters were found guilty today of every charge they faced - 13 counts of rape, kidnap and false imprisonment.
Three other teenagers pleaded guilty to rape, kidnap and false imprisonment before the trial.
An order currently prohibits publishing the identities of the teenagers.
Following the verdicts, which the jury returned after 14 hours and 51 minutes, three of the defendants stormed from the dock in disbelief. Several of their parents were seen sobbing in the public gallery.
After ordering them to return, Judge Wendy Joseph QC told them: 'This is a tragedy not only for your victim, who I think you now understand will never get over this, but it's a tragedy for you too.
'One of the things I think is so sad about this case is I'm absolutely sure that she was telling the truth when she said that (one of you) said you could not help her because you were with your boys now.
'Essentially it wasn't about you setting out to do what you did, it was about you setting out to stick with your mates.
'You have each been convicted of a terrible series of crimes and the only sentence I can pass will be one of custody.
Judge Joseph ordered pre-sentence reports, adding: 'They are very young - I want to know what's been going on in their backgrounds.'
A 16-year-old defendant denied kidnapping, false imprisonment and three counts of rape.
Four other 16-year-olds and a 14-year-old denied false imprisonment and two charges of rape on April 30 last year.
They were convicted of every charge.
They all face years behind bars.