Fourth person of interest identified in William Tyrrell case

William Tyrrell, 3, disappeared while playing hide and seek with his sister.

Police have reportedly questioned a fourth person of interest over the disappearance of NSW toddler William Tyrrell.

They have spoken to an elderly man living on the state's mid-north coast in relation to the missing boy, the Daily Telegraph reports.

The man reportedly denied having anything to do with the disappearance, telling the newspaper he was listed on the child protection register and believed he was visited by police for that reason.

William vanished without a trace from his grandmother's front yard in Kendall on September 12, 2014.

A NSW Police spokeswoman said the force would not comment on who may or may not be persons of interest in the disappearance because the investigation was ongoing.

Solving William's disappearance remained a priority for police, the spokeswoman said.

"It doesn't sit well with us, particularly at this time of year, that we still don't know what happened to William," she told AAP.

"Any information, no matter how seemingly innocuous it may appear, could be vital to us in solving this mystery."

- AAP