NEW YORK — Experimentation with human growth hormones by America’s teens more than doubled in the past year, as more young people looked to drugs to boost their athletic performance and improve their looks, according to a new, large-scale national survey.

In a confidential 2013 survey of 3,705 high school students, being released today by the Partnership for Drug-Free Kids, 11 percent reported using synthetic HGH at least once — up from about 5 percent in the four preceding annual surveys. Teen use of steroids increased from 5 percent to 7 percent over the same period, the survey found.

Travis Tygart, CEO of the U.S. Anti-Doping Agency, depicted the numbers as alarming but not surprising, given the extensive online marketing of performance-enhancing substances and near-total lack of any drug testing for high school athletes.

“It’s what you get when you combine aggressive promotion from for-profit companies with a vulnerable target — kids who want a quick fix and don’t care about health risk,” Tygart said in an interview. “It’s a very easy sell, unfortunately.”

Nine percent of teen girls reported trying synthetic HGH and 12 percent of boys.

“A picture emerges of teens — both boys and girls — entering a largely unregulated marketplace (online and in-store) in which performance-enhancing substances of many varieties are aggressively promoted with promises of improved muscle mass, performance and appearance,” said the report.