Survival window closing for missing NSW boy

Police have not given up hope for missing NSW three-year-old William Tyrell but say the survival window is closing as the desperate search enters its fourth day.

Superintendent Paul Fehon told reporters today the search was still focused on the area with 1.5km of where William vanished at his grandparents' home on the NSW mid-north coast.

"As time goes on, of course, the odds of survival decrease," he said.

"That window (of survival) is still there according to our advice."

Police have still not discovered a trace of William since he disappeared, wearing a Spider-Man outfit, on Friday morning.

The family have released new photos of William to help in the search.

Supt Fehon said the family was coping well under the circumstances but was still doing it tough.

"Their hope is actually despair at times," he said.

However, he said searchers, including police and volunteers, "had not even considered" giving up hope of finding William.

He would not comment on reports police had canvassed sex offenders in the area, but said the hunt for William included a "search aspect" and an "investigation aspect".

Fears are growing the boy has possibly been kidnapped.

Supt Fehon also praised the volunteer searchers, some of whom had come from as far as Lismore.