More than 20 search and rescue volunteers have bolstered the search for a missing paua diver near Titahi Bay, Porirua.

Police believe father-of-three Colin Smithies, 49, of Wellington, may still be alive, despite last being heard from at 6pm on Monday when he texted his partner he had found a good dive spot.

His backpack was found about 1km south of Titahi Bay beach, which provided search teams with a point of entry into the water.

The search for Mr Smithies resumed at first light today, with Wairarapa and Wellington volunteers set to do land and shoreline searches from Rocky Point in the south to Pukerua Bay in the north.

They join a search team including the Wellington Police Maritime Unit launch and the Police National Dive Squad.

About 40 people in total are now involved in the search, which began at first light yesterday.

The officer in charge of the operation, Inspector Mike Wright, said he was holding out hope Mr Smithies was alive.

"In operations like this, we're always hopeful we'll find the missing person alive, however we must keep all of our options open and remain focused on continuing a thorough search of the area."

Yesterday, Mr Wright said Mr Smithies, who was wearing a wetsuit, was a confident swimmer and an experienced diver who had a "pretty good" chance of survival.

Mr Smithies is a former publican in rural Southland who made a remarkable career change to become a university lecturer in economics.

Originally from Whanganui, he spent 18 years in the hospitality industry, including a stint at Pizza Hut, and about 13 years ago was working as a bar manager at a Tapanui pub, between Invercargill and Dunedin.

Mr Smithies told Radio New Zealand, as one of series of 2008 interviews on career changes, that while Tapanui was a wonderful place for hunting and fishing, he got sick of drunks, fights, the hours, and he didn't want to just focus on getting people drunk.

"My greatest fear was I was going to get someone under the weather and they were going to drive and kill someone."

Despite having failed to pass his papers at a previous university stint, he returned in 1997 as an economics student.

Returning to university was "scary", he said, because he saw the young fellow students and thought "I have pubic hair older than most of these kids".

However, he focused on his work and getting out of the education system as much as he could.

He earned A pluses and found he loved mathematics. He stayed on at the university to lecture in economics.

Mr Smithies said he loved teaching economics and drew on his own history working in bars to teach the subject.

He left Otago University about two years ago to take up a position with the Commerce Commission in Wellington as a senior economist.