Billboards showing the image of missing toddler William Tyrrell are being erected along a major NSW highway as the hunt for the boy in the Spider-Man suit continues.

The three billboards will go up alongside the Pacific Highway from Tuesday.

A poster seeking information about missing toddler William Tyrrell issued by the Where?s William? campaign. Credit:www.whereswilliam.org

Featuring a photograph of four-year-old William, the white, blue and red boards will be concentrated on the Mid North Coast stretch, including near an exit to Port Macquarie.

Two will be placed just north of Taree.