A team led by Malaysia with investigators from various countries including the United States, Britain, China, France and Australia is due to release an interim statement on their inquiry into the cause of the disappearance on Sunday.
The Malaysia Airlines Boeing 777-200ER disappeared on a flight from Kuala Lumpur to Beijing with 227 passengers and 12 crew on board. It has become one of the greatest mysteries in aviation history.
"The disappearance of MH370 is without precedent, and so too is the search – by far the most complex and technically challenging in aviation history," Najib said in a statement.
"Together with our international partners, we have followed the little evidence that exists. Malaysia remains committed to the search, and hopeful that MH370 will be found," he said.
Investigators believe the plane was flown thousands of miles off course before eventually crashing into the Indian Ocean.
Some of the relatives of those on board have been holding vigils this weekend to mark the anniversary.
In Beijing, police scuffled with some family members offering prayers at a temple as they tried to talk to foreign reporters, Reuters reported.
"I can't sleep at night, each night I'm only getting about two hours, but I'm certain that my daughter is still alive and I'm going to get her back," said one mother, who did not give her name, before being escorted away.
Family members have previously described harassment by police, who are nervous about any threats to social stability.
The Chinese government, however, says it will provide whatever help it can to the relatives and it offered its sympathies on the anniversary.
China's foreign minister said the search for the aircraft would not stop.