Search and rescue teams, the police maritime unit and the police helicopter were unable to find the man last night.
The search was suspended about 10pm, and resumed at first light today.
Sergeant John Saunders of the Auckland police maritime unit said the police national dive squad would join the search today.
Their first task would be to establish whether the man had fallen off the ketch.
"We don't actually know what's happened to him. A dinghy was found ashore and he wasn't on the boat, and he hasn't returned home," Mr Saunders said.
"There is a possibility he has fallen off his boat, so that's why we have to go and have a look."
If the man was not found near the ketch, police would then look into the significance of the dinghy found ashore.
Mr Saunders said suspicious circumstances were not being considered at this stage.