The other three-quarters ate meals with the family three to six times a week (41 per cent) or at least seven times a week (35 per cent).
Lead author Dr Jennifer Utter said there was worldwide concern about family meal patterns because of social changes such as more mothers going out to work, the spread of fast food and more teenage distractions such as TV, computer games and other activities.
"Families sometimes have difficulty with scheduling issues if you have active young people who are not home a lot because of other activities, or if you have parents who are working shift work or doing multiple jobs," she said.
The survey found that teenagers were also more likely to eat separately if they live in more than one home (27 per cent eat with family less than three times a week), in sole-parent homes (28 per cent) or in homes with an unemployed dad (33 per cent).
"Young people with unemployed fathers have lots of other stresses in their households and sitting down to eat meals together may not be top of their priorities," Dr Utter said.
Unsurprisingly, teens who often ate with their families were more likely to say they could talk to their mothers and fathers about their problems or worries, and that their parents always wanted to know where they were.
Measures of wellbeing increased, and depression scores decreased, as the number of meals they ate with their families increased.
Eight per cent of those who ate together less than three times a week had attempted suicide in the past year. But the figures were only 4.1 per cent for those who ate together three to six times a week, and 2.9 per cent for those eating together at least seven times a week.
The clinical director of Counties-Manukau child and adolescent mental health, Dr Peter Watson, who led the first youth survey in 2001, said the findings were not surprising but would be valuable for parents.
"One of the recommendations for families is that if they can eat meals as a family and swap notes and problem-solve, those are really important strategies," he said.
"Especially where people are having struggles or issues with their emotional wellbeing, it becomes even more important that those kids are heard by their parents and there are good quality conversations between parents and kids."