Police Scotland's dog branch and air support unit have been deployed in the Irvine area in an effort to trace Gordon Speirs.
His disappearance was said to be totally out of character.
Mr Speirs is described as being 5ft 10in tall, of medium build, with red hair and blue eyes.
At the time of his disappearance he was wearing navy coloured combat trousers, a black waterproof jacket and timberland boots.
Insp David Carballo of Ayrshire Police Division said: "This is totally out of character for Gordon and his family are understandably very worried.
"With the deteriorating weather conditions and concerns for his health, we are keen to have him back home safely as soon as possible.
"I am appealing to anyone who may have seen him or indeed for Gordon himself to contact us by calling 101."

It took 72 firefighters five hours to extinguish the fire in Trebovir Road, Earl's Court, after being called at about 21:45 BST on Sunday.
They rescued 12 people from inside the building, three from one next door and two from the roof of a neighbouring property.
Nobody was hurt but 150 people were evacuated.
The whole of the second floor of the hotel was damaged by fire, three quarters of the third floor and all of the roof.
Station manager Winston Douglas said: "This was a serious fire and crews and worked very hard to stop the fire spreading."

UKIP, which won May's election, spent £2,956,737, while the Tories' campaign expenditure was £2,980,815,
The Lib Dems spent £1,580,575 and lost all but one of their MEPs - Labour, which came second, spent £1,027,339.
The figures cover the campaign period from 23 January to polling day, 22 May.
UKIP's campaign spending works out at 68p for each of their 4,376,635 votes. For Labour it is 26p per vote, the Conservatives 79p and the Lib Dems, who lost 11 of their 12 MEPs, £1.45. The Green Party, which came fourth, spent £534,249 on its campaign - 43p for each of its 1,255,573 votes.
Including the SNP's £267,372, the six highest-spending parties spent a total of £9,347,087 on campaigning, the Electoral Commission said.
All but Labour spent more than they did during the 2009 European election campaign.
Police have launched an extensive search for a 53-year-old man who has been missing from his home in North Ayrshire since Thursday morning.
[NEXT_CONCEPT]
Seventeen people were rescued after a huge fire ripped through a hotel and block of flats in west London.
[NEXT_CONCEPT]
The UK Independence Party spent almost as much as the Conservatives at this year's European elections - while the Lib Dems outspent Labour, Electoral Commission figures show.