Watch the sickening attack by a gang of youths that's left a teen too afraid to leave the house or return to school

A teenage boy has been left 'traumatised' and fearing for his life after a shocking attack on him by a dozen others on his way home from school in Sydney south-west.

Not only did the thugs assault the 15-year-old, they filmed themselves doing it, with the video now being a major part of a police investigation into last Wednesday's incident.

The confronting footage began with the teen trying to de-escalate the situation while surrounded by several youths at Chester Hill train station.

'I haven't touched you. I haven't done anything,' he's heard pleading.

But while he was distracted, a young male with a ponytail coward punched the victim twice as several others joined in on the ferocious beating.

The Sefton High School student managed to escape but the pack of thugs chased after him and hunted him down.

'I tried to escape by running to the park next to the station and I lost my balance and fell on the ground,' the student told Nine News .

Then the attack started again, with the person filming the merciless attack also taking a turn to kick the boy, who was lying helpless on the ground.

'They were ... more than 10 people,' the student said.

Police were called to the scene but by then, the thugs had already fled.

'The boy was treated at the scene by NSW Ambulance paramedics before he was taken to Bankstown Hospital' a NSW Police spokesperson told Daily Mail Australia.

The teen spent the night in the hospital and the police are now trying to track down his attackers.

The boy's father hopes his son's attackers are caught and that no other family has to go through something like this.

'Make sure this never happen again in the future at any school in this area or even in Sydney,' the dad said.

His son doesn't want to be identified as he's afraid the gang will target him again.

The sickening assault has made him too fearful to go back to school or even out to the shops.

He doesn't even want to watch the video of the attack.

'I don't dare to watch the video. I'm mentally traumatised,' he said.

Police investigations continue.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000.