Police confirmed yesterday they were looking for Colin Smithies (49), who left Dunedin for Wellington in 2009 to work as a senior economist with the Commerce Commission.
More than 40 searchers scoured the area around Titahi Bay, Porirua yesterday.
Mr Smithies' wife last heard from him at 6pm on Monday, when he texted her to say he had found a good diving spot, Inspector Mike Wright told a media conference yesterday.
When Mr Smithies did not return home, his wife contacted police at 11pm to report him missing.
A large aerial and water search, involving dozens of search and rescue volunteers, three coastguard vessels, a rescue helicopter, a police launch and a specialist dive squad, began around Titahi Bay at dawn yesterday.
Mr Smithies' backpack, which contained a cellphone and wallet, was found 1km south of Titahi Bay beach, and his car was parked in Titahi Bay.
An area from Rocky Point in the south to Pukerua Bay in the north, including Mana Island, was being searched.
Mr Smithies was wearing a wetsuit and was considered to be an experienced diver, although was not overly familiar with the area.
"We believe that he could easily be alive now if he is still in the water," Insp Wright said.
The search prompted police to remind people to always dive with a buddy.
Family friend Lisa Scott, of Dunedin, said she was devastated to hear he was missing.
However, she remained optimistic this "renaissance man" would survive.
"If anyone would roll up and say 'Sorry I am late', it would be Colin."
In a 2008 interview with Radio New Zealand, Mr Smithies spoke about his move from a hotel in Tapanui to academia, and his fondness for hunting and fishing.
He moved from the West Otago township 14 years ago after becoming disillusioned with the downside of the hospitality industry: drunks, fights, and the fear of a patron killing someone if they drove home drunk.
In his mid-30s, he moved to Dunedin with his family to have another crack at tertiary education after failing to pass a paper in an earlier stint.
Despite finding being a mature student "scary", he excelled, earning top marks and the chance to teach economics.
"I just love teaching economics," he said.
A doctoral student at Otago, he left in early 2009 to take up the job in Wellington.
A Commerce Commission spokeswoman said he was an "ebullient personality" who used his cooking skills from his time in the hospitality industry to good effect.
Mr Smithies is the father of young children and two adult children from a previous marriage.
- Additional reporting NZPA
