The body of a teenage boy has been found on the side of a road in bushland in Sydney's south-west.

A passer-by found the boy lying next to Wilton Park Road, in Wilton, just before 7:30am on Saturday.

Police have set up a crime scene and have closed the road in both directions.

The boy is yet to be formally identified but is believed to be a teenager.

Police are treating his death as suspicious and are calling for anyone who may have relevant information to contact them.

They are specifically calling for anyone who was in the area from 6pm on Friday and may have relevant dashcam or mobile phone vision to come forward.

People are urged to contact Camden Police Station or Crime Stoppers on 1800 333 000.

Police are expected to provide more information this afternoon.