Two teenage girls who had become lost after skipping school to go shopping in Castle Hill were lured off a train and sexually assaulted in broad daylight on Tuesday, police say.
Police are hunting for three men who struck up a conversation with the 16-year-old school friends on a train near Blacktown and convinced them to get off at Fairfield and go to a park where they were allegedly sexually assaulted.
Detective Superintendent Peter Lennon said it was likely police would learn the identities of the men and he urged them to come forward ''before we come knocking on their door''. Sydney Trains and Sydney Buses have been contacted to provide CCTV of the group.
Police have also appealed for a person out walking a dog in Fairfield Park on Ulverstone Street between 1pm and 2pm to come forward.
The girls, both from western Sydney, had skipped school for the day and were trying to get to Castle Hill but were lost near Blacktown, Superintendent Lennon said.
They were asking people on the train for help and the three men, thought to be in their late teens and early 20s, struck up a conversation with them for about half an hour.
They then coaxed the girls off the train at Fairfield under the guise of taking them to the right bus terminal.
The girls were allegedly sexually assaulted in a secluded part of Fairfield Park behind a grandstand.
The group left the park together before the girls were able to get away to seek help from a passer-by.
''The girls would have been absolutely upset and traumatised,'' he said.
They were taken to hospital for treatment and have given statements to police.
''It's very brazen. It's something that is absolutely unforgivable in the local area,'' Superintendent Lennon said.
Neighbours said the football field's dilapidated grandstand is a popular spot for teenagers skipping school.
''Every day they come at 9.30am and go at about 2.30pm,'' said a neighbour, Elly. ''It happens all the time.''
On Wednesday morning, detectives were doorknocking nearby homes and searching for CCTV footage of the attackers, whom they described as being Middle Eastern in appearance.
One man was described as being about 19 to 21 years old, about 178 centimetres tall, with a dark complexion, a thin build and dark hair.
A second is about 175 centimetres tall, with a thin build and black hair.
The third is described as being between 17 and 19 years old, with a medium build and about 175 centimetres tall.
Anyone with information is urged to call Crime Stoppers on 1800 333 000.