Detective Dougall Henderson, of Invercargill Police Search and Rescue, said police were notified on April 24 that the 7.5m Munetra was overdue.
A man and two women were on board when it left Bluff on April 16 for Preservation Inlet, in Fiordland.
The caretakers of Preservation Lodge, where the trio were headed, told police the group had not arrived, Det Henderson said.
No communication had been made with the yacht since it left Bluff. It had a marine radio and those on board had cellphones.
It was due back in Bluff on April 22.
A fixed-wing Coastguard plane flew over the area yesterday afternoon but had not spotted the yacht, Det Henderson said.
''We are having difficulty with the start point [for the search] because it's now nine days since anyone has seen or heard from them ... and they could be anywhere.''
Helicopters would join the search effort today.
Commercial and recreational boat users had been told of the missing vessel but few were on the water yesterday because of the weather, which had hampered efforts, he said.
The names of the trio would not be released until their next of kin had been notified. Anyone who might have seen the yacht was urged to contact police, Det Henderson said.
