A third of boys, aged 11 to 16, said they wanted to become more muscular to look like their favourite stars on TV.
While it is widely known that young girls are very body conscious, the news that boys are also comparing themselves to celebrities is a surprise.
"It is interesting that what used to be seen as a problem affecting young girls has now spread to young men," said Rosi Prescott, chief executive of Central YMCA, which commissioned the study of 810 youngsters, aged 11 to 16.
"The root cause of this problem is the pressure on young people to conform to an unattainable and unrealistic body image ideal."
The study also found that half of girls said they wanted to be slimmer and that they would resort to diet pills, laxatives, cosmetic surgery to achieve their idea of the perfect body.
"Young people appear to be increasingly insecure about their appearance and body image," said Rosi Prescott.
"There is a growing trend to resort to quick fixes, which are damaging to health and often unfulfilling.
The survey is published on the same day an all-party group of MPs will begin an inquiry into body image in the UK, including anorexia, obesity and self-harm. Earlier this year, a survey blamed celebrity culture, the fashion industry and advertisements fuelling the obsession with being slim.
Do you think boys and girls are under unbearable pressure to look good?