A man has surrendered to NSW Police after his photograph was publicly released over allegations he groomed and sexually assaulted a teenager in Sydney.

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Man charged with alleged child sex abuse

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VIDEO A man has been charged over the alleged sexual assault of a young girl in a Sydney oval. Man charged with alleged child sex abuse

Detectives on Monday said State Crime Command's Child Abuse Squad hadn't been able to identify the man, who first befriended the girl online when she was 14 in 2015, despite months of investigations.

It's alleged he sexually assaulted her at an oval in Hornsby Heights between February 2015 and January 2016 after their relationship continued.

The 37-year-old handed himself in to officers at Chatswood Police Station on Monday afternoon after his photograph was released.

A 37-year-old man faces child sex offences after he handed himself in to police following assaults on a girl in a park. Photo: 7 News

He was questioned and charged with multiple child sex offences including 12 counts of sexual intercourse with person aged 14 to 16 and nine counts of engaging in acts of child prostitution.

The man, from Chatswood, has been refused bail and will appear appear at Hornsby Local Court on Tuesday.

The incident prompted Detective Acting Superintendent Peter Yeomans to warn parents to speak with their children about online safety.

The assaults happened in a northern Sydney park. Photo: 7 News
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