The Nina, a wooden racing vessel built in 1928, was last in contact with authorities June 4, at which point it had hit rough seas, The New Zealand Herald reported Friday.
The boat, which was carrying a crew of six Americans and one Briton, left a port in Opua the previous day and was about 400 miles north-northwest when it got into trouble.
Rescue Co-ordination Centre coordinator Kevin Banaghan said he has "grave concerns for the Nina and her crew, but remains hopeful of a positive outcome."
"Our records show that conditions at the last known position for the vessel were very rough, with winds of [50 mph], gusting to [68 mph], and swells of up to 8 meters [26 feet]," Banaghan said.
In mid-June, maritime authorities in New Zealand carried out air searches of the water looking for signs of the Nina or its crew, but came up with nothing, CNN reported.
Now, a plane will scour New Zealand's beaches, looking for the boat's life raft or any other wreckage.
"While we have grave concerns for the crew on board Nina, we have not given up hope of finding survivors," said mission controller Neville Blakemore.