Police say the last known sighting of Ira Shephard, whose body was found in Tauranga Harbour on Saturday, when he was still alive was in late November.
Mr Shephard, 29, was last seen by an associate on Friday, November 30.
It was not clear how long his body had been in the water, police said.
They were keen to find out about his movements and his demeanour in the days leading up to November 30, and anything since then.
An autopsy was carried out yesterday and his death was being treated as unexplained, as opposed to suspicious, police said.