New South Wales police said the teenager was arrested on Saturday evening after Strike Force Mexvo was established to investigate a spate of alleged incidents on walking trails in the Narrabeen area during the first weeks of October.
Police allege the boy committed 11 separate offences against girls and women aged between 13 and 54. He was charged with three counts of behaving in an offensive manner in or near a public place and eight counts of sexually touching another person without consent.
The investigation began after three separate alleged incidents reported on 7 and 8 October. In each, a male allegedly approached women on walking trails, sexually touched them and then rode away on an ebike. In one case, the offender allegedly made inappropriate sexual comments.
An earlier incident was also reported: on 1 October near Narrabeen lagoon, a woman was allegedly sexually touched before the suspect rode away on an ebike. On Monday 12 October, police received a report that between 5pm and 5.30pm two women walking along the lagoon near Bilarong reserve had been sexually touched by a male riding an ebike.
Police had released CCTV images of a male they believed could assist with inquiries before the boy attended Mona Vale police station about 7.30pm on Saturday. He was taken to Manly police station and charged.
Supt John Duncan, speaking in Narrabeen before the arrest, urged the public to provide information, noting the bushland park stretches 8km with limited CCTV coverage.
The 13-year-old was granted conditional bail and is scheduled to appear at children's court on 4 November.