William was last seen wearing a Spiderman costume on Friday, September 12 at 10.30am as he played with his sister in the front yard of their grandmother's home on Beneroon Drive, Kendall.
Police, SES volunteers, RFS volunteers and community members spent 11 days searching areas spanning 48 kilometres.
Police have since set up a task force to help find William and are asking for the public's help.
"There's no information that's too trivial or irrelevant or embarrassing to somebody, it might be the key that’s going to help us find young William," Acting Superintendent Tony Joice from the Mid North Coast told the Today Show's Sylvia Jeffreys.
Anyone with information, is urged to call Crime Stoppers on 1800 333 000.