A 37-year-old man has been charged after a teenager was allegedly sexually assaulted in Sydney's upper North Shore two years ago.

Police questioned the man over the incident after he attended Chatswood Police station on Monday afternoon, hours after they launched an appeal to the community.

According to police the then 14-year-old girl had begun communicating with a man online in early 2015.

Police claim the girl met him on a number of occasions between February 2015 and January 2016 at an oval in Hornsby Heights, where they reportedly had sex. 

The man was charged with twelve counts of sexual intercourse with person aged 14 to 16 and nine counts of engaging in acts of child prostitution. 

Child Abuse Squad commander, Acting Superintendent Peter Yeomans, said it was a timely remainder to parents about their childrens online safety.

"Any app, online game, or social media platform that allows the user to be in contact with someone they've only met online potentially puts them at risk.

"Not only should young people be very careful about providing personal details to a person they only know in online environment, they should never organise to meet as doing so may place them at further risk of harm."

Mr Yeomans thanked the media and community for their ongoing assistance and support.

The man will face Hornsby Local Court on Tuesday.