The wife of a 79-year-old man with Alzheimer's missing in dense bushland Sydney's north for more than two days has made an emotional appeal for help.
Police are spending a third day searching for Ronald Weaver, who was last seen on Woolcott Avenue in Wahroonga at 10am on Tuesday.
The search is focused on bushland at Cliff Oval in the suburb.
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Weaver's wife Hannah urged locals to "remember his face" from police photos.
"He's a good person, even though he has Alzheimer's I believe he still deserves quality of life," she said.
"Please, please help to locate Ron.
"He remembers his name, even though he doesn't remember his date of birth."
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Around 100 people are involved in the search, including the NSW Police dog, mounted and trail bike units, SES, PolAir, NSW Rural Fire Service and National Parks and Wildlife Service staff.
Acting Superintendent Carlene Mahoney asked locals to check around their houses.
"We urge people in the area to look in their backyards, sheds, driveway and you may find Ron has taken shelter from the heat over the past few days," she said.
"Time is critical.
"We've been searching for the last three days and we're urging the public to search their areas and if you're out on the trails please look out for Ronald."
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Police are also doorknocking local homes and asking people to check any CCTV they have.
A targeted SMS message has also been sent.
Weaver is described as Caucasian, about 155cm to 160cm tall, thin with grey hair which is bald on top.
He was last seen wearing a cream-coloured shirt with a Sapporo beer logo, grey shorts and striped socks.