The grandaughter of missing Orewa man Mike McClennan says he's a "kind, social, Kiwi legend who would stop to chat with anyone".

Photo: Supplied / NZ Police

Seventeen-year-old Katie McClennan is pleading for the public to keep an eye out for her 75-year-old grandfather, who disappeared from Milton Court Rest Home on Wednesday and was last seen walking north on the Hibiscus Coast Highway.

Mr McClennan is well-known in rugby league circles and is the father of former Kiwis and Warriors coach Brian McClennan.

Ms McClennan said he was likely wearing a red and black St Helen's jacket, blue jeans and black Sketchers shoes. He suffers from dementia, and sometimes thought he was in jail, she said.

"That makes it really difficult because he probably just tried to escape and when the police go by - and the police have done amazing work - he's probably trying to hide from them," she said.

She said her family had been looking relentlessly, but they're worried he might have hitchhiked or become lost.

"I've been out there looking, my whole family is up, from everywhere [in the country] trying to look for him," she said.

"He recognises his family so I would just hope that he'd see me, and if he's stuck somewhere, try to get out."

Despite her family's concerns and fears, she said the support from the local community had been "unreal".

"People are bringing everything we need. They've been searching day and night. I mean that the Hibiscus Coast community is just rallying ... getting involved, helping us every step they can," she said.

"I can't even explain how thankful we are."

Search and rescue teams and a helicopter have spent the past two days combing the area for any sign of Mr McClennan.

A statement from police said they were aware members of the public were keen to help in the search, and they were welcome to do so along the public walkways in the parks and beaches around Orewa.

Senior Sergeant Brett Henshaw said they wanted to hear from anyone who may have seen Mr McClennan, and they have asked drivers to go back through their dashcam footage if they were in the area where he was last seen.

"This is a race against the clock, we're over 40 hours now, he's a 75-year-old man, he's on medication, this is getting critical for him."

Locals have been asked to check their backyards, sheds and holidays homes for anything that may help with the search.

Anyone who has information or sees Mr McClennan should call 111.