Senior Sergeant John Fookes, of Queenstown, said Mr Duncan (46) went missing from his cabin boat, Sundance 2, on Sunday.
''Mr Duncan, known as Matt, is the owner of Painting Solutions and had been working at Queenstown,'' Snr Sgt Fookes said.
The Police National Dive Squad arrived in Queenstown late yesterday morning.
Snr Sgt Fookes said divers would search an area from the Earnslaw slipway, where the boat set out about 9.30am on Sunday, to near the Bay View Rd boat ramp.
It had then either drifted or made its way towards the shore, Snr Sgt Fookes said.
Late on Sunday afternoon the boat was found to be empty and the man missing.
LandSAR and Coastguard personnel searched the shoreline and lake on Sunday night.
The search resumed on the water, around the shore, and from the air, on Monday.