Three men have been found guilty of the gang rape of a teenage girl that was filmed on a go-pro camera at a house party in western Sydney.

Tristan Carlyle-Watson, 26, Kurt Stevenson, 26, and Andrew Waters, 25, had been on trial in the Downing Centre District Court for the sexual assault, which happened at a house party at St Clair in Sydney's west in May 2015.

Police only learned of the incident two days after it happened when they stumbled upon the Go-Pro camera while investigating a graffiti crime.

The girl, who was 16 at the time, did not make a complaint until detectives tracked her down several weeks later after identifying her from the footage.

Crown prosecutor Sharon Harris told the jury the girl had been invited to the party by Carlyle-Watson whom she had befriended a few days earlier on Facebook.

Ms Harris said the teenager was scared to go to a party where she would not know anyone, but Carlyle-Watson said he would give her a lift there and "take care of her".

It was the Crown's case the girl was drinking alcohol and smoking cannabis prior to the sexual assault and became intoxicated to the point of blacking out.

Ms Harris said the 17-minute-long video showed the men sexually assaulted her, "sometimes simultaneously, sometimes taking turns".

The court was told the girl was unaware of the sexual acts that had occurred and had no idea she was being filmed, but she did remember being in the bathroom and discovering lots of blood.

When a friend came to pick her up she was naked and covered only by a towel.

All three men pleaded not guilty to aggravated sexual assault in company.

Their barristers argued the group sex was consensual and the video showed the girl enjoying it, however the Crown argued she was too intoxicated to be able to freely and voluntarily give her consent.

After a six-week-long trial, the jury deliberated for just over three days before delivering the guilty verdicts.

The men will return to court for sentencing in October.