Rescuers in New Zealand were alerted on June 14 after family members of the crew raised the alarm.
They began trying to make contact with the vessel, but were said not to be unduly concerned as it was fitted with an emergency locator beacon which had not been activated, as well as a satellite phone and spot beacon.
Aerial searches of the area began on June 28, and two extensive sea-based searches as well as two shoreline searches failed to locate the boat or the crew.
The crew included seasoned skipper David Dyche, 58, who was on board with his wife, Rosemary, 60, and their teenage son David.
The Dyches have sailed the Nina around the world, while David senior has captained boats almost his entire life.
Born in London, Matt is a classically trained cellist and committed vegan. He is credited with rebranding The Green Party in 2004, and moved to Lancaster shortly after.
He stood in the 2005 county council elections for Lancaster East, coming second, and he also stood in a city council by-election in John O’Gaunt Ward in 2006/7.
He worked as press officer for former Lancaster digital art media organisation Folly between 2006 and 2008, and embarked on his trip in 2010, visiting the Americas, before heading out across the Pacific.
His mother Susan, 62, said: “We are on the internet every minute of the day trying to find some news.
“We just want the New Zealand coastguard to keep on looking for the boat.”
Coun Jon Barry, who Matt lived with for a while in Lancaster, said: “Matt was a person with enormous amounts of energy. He was also very talented both as a musician and as a media and publicity operator.
“If, as seems likely, he hasn’t survived the boat trip then it is a very sad day for environmentalists in Lancaster. However, knowing Matt, I haven’t completely given up hope that he will somehow pop up again.
“If anyone can, he can.”