Quoted by BBC Health News, "The Information Standard – a government-backed scheme to improve the reliability of health information – surveyed 1,200 18-24-year-olds.
The research showed eight in 10 relied on the internet for help without being aware of the authenticity of the sites.
Experts said it was essential the young sought help from official channels.
Nearly two-thirds of participants reported never having had a sexual health screening.
Their reluctance to use official NHS services was blamed on embarrassment and a lack of awareness about the seriousness of conditions.
Informed advice
Where young people do rely on the internet, the Information Standard said it was important to use reliable sites, such as those produced by the NHS, local authorities or leading charities.
Official and authenticated sites carry the Information Standard brand.
Ann Robinson, director of public awareness at the Information Standard, said: "We want all young people to understand how to spot a trustworthy site.
"Just because it ranks high in the search engine, for example, does not mean that it will provide informed advice."
Dominic Edwardes, of the Terrence Higgins Trust charity, said: "Sexually transmitted infection rates are worryingly high amongst young people, accounting for more than half of all new diagnoses in England in 2010.
"To reduce these figures we need to make sure that young people are equipped with trustworthy advice and understand how to have safe protected sex."
