The Australian Missing Persons Register reported the incident on its Facebook page earlier this month, after noticing the 'fundraiser' on one of the social media pages set up to find the little boy.

The register's administrator wrote that the 'fundraiser' asked for cash donations and for people to buy wristbands to support William's family.

But the family do not want such support, have not been provided with any donated money and never authorised such fundraising.

'Please do not send any money of any kind to any William Tyrrell group, as I have it first-hand that there is to be NO fundraising done of any kind, it is not required,' the administrator wrote.

She also alleged that the woman running the page had stated she would be keeping the money.

The Australian Missing Persons Register has since been contacted numerous times for comment but did not respond.

A NSW Police spokeswoman said such scams are "not uncommon".

"Police urge members of the public to always check a charity or fundraiser is legitimate before donating."

The spokeswoman said she was not able to find any reports about the alleged fraud, "but would urge any person who believes a fraud is taking place to report the matter to police".

As part of Fraud Week, Senior Constable Steve Cherry reminded the community that "these days criminals don't need to necessarily meet you in person to steal from you".