The girls, two aged 17 and one 16, were convicted of false imprisonment and causing a person to engage in sexual activity without consent.

The victim, now 18, was stripped, punched and kicked while the girls filmed the attack in March last year.

The three will be sentenced on August 30, Inner London Crown Court heard.

One of the girls was acquitted of kidnapping and all three were acquitted of theft.

A fourth girl, aged 17, was acquitted on all counts and cried as she left the dock.

Judge Colin Smith said that it was "a prolonged ordeal of the most unpleasant nature".

The victim was 17 at the time when he was dragged to a flat in Woolwich by one of his attackers who accused him of owing her money.

They made him perform a humiliating sex act while "they were baying like a pack of hyenas", he said.

The court's finding will send out a clear message

DC Neil Perkin

After the brutal ordeal, he said his clothes, which had been thrown off a third-floor balcony during the assault, were returned to him and he was allowed to dress and leave.

He told the court he could not escape because of a leg injury and because his upbringing "not to hit women" made it impossible to fight back.

The police paid tribute to the victim's "bravery and courage".

"The perpetrators filmed these crimes, commonly known as 'happy slapping' videos," said Detective Constable Neil Perkin.

"The court's finding will send out a clear message to all those who participate and involve themselves in filming unlawful predetermined violent acts."