Three men found guilty of raping teen girl and filming assault with a Go-Pro.

Three men have been found guilty of gang raping a teenage girl at a western Sydney house party after police found footage of the assault on a GoPro camera.

A jury at the Downing Centre District Court on Tuesday found Tristan Carlyle-Watson, 26, Kurt Stevenson, 26, and Andrew Waters, 25, guilty of aggravated sexual assault in company.

During the trial, crown prosecutor Sharon Harris said the 16-year-old girl was drunk and believed she had been drugged before the assault at the St Clair house in May 2015.

Tristan Carlyle-Watson. (Image via Facebook.)

In a 17-minute-long video, Ms Harris said a group of men sexually assault the girl, "sometimes... simultaneously, sometimes taking turns."

One man is heard saying "One by one we'll all get a f***," she told the court.

The victim has "slow movements, floppy limbs" and repeatedly says she's tired and wants a blanket, Ms Harris said.

"Kurt Stevenson has to direct her to take her clothes off or to move or sit up," she said.

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"They don't speak to her other than Kurt Stevenson who seems to be, you might think, pacifying her."

The teenage girl was unaware of what had happened until six weeks after the party when police knocked on her door and said they had found GoPro footage of her being assaulted.

She has no memory of the rape and has not seen the video, Ms Harris said.

The trio is due to be sentenced in October.