The search for missing Torbay woman Patricia Wearn has entered its fourth day, as defence force staff join those looking for the 73-year-old.

Wearn, who has Alzheimer's, has not been seen since she left her Torbay home for a walk on Monday.

A large-scale operation with police search and rescue and LandSAR volunteers has continued since.

Sergeant Dene Duthie, officer in charge of the search, said several ponds and waterways near Wearn's home were searched by the National Police Dive Squad.

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Nothing was found.

Additional search and rescue staff from Waikato have arrived to help.

Members of the defence force, including those from the navy and airforce, had joined others searching bush areas around Torbay.

Police officers are also continuing to go door-to-door to speak to residents and search properties.

Wearn's family asked police to share their thanks to the public for their support and good wishes.

"They say the past four days have been long and stressful and whilst they are grateful for the public support, at this point they don't wish to make any further comment in the media, or on social media."

Anyone with information related to Wearn should contact police.