Three-quarters of 11- to 16-year-olds in the UK have a mobile that can access the internet, and the number is rising rapidly: only a year ago the figure was 65%. More children and young people than ever – some 74% of five to 16-year-olds – have their own laptop or PC and 58% can now access the internet in the privacy of their bedroom. Those figures are up from 62% and 46% respectively just a year ago.

In that context it's no surprise that local authorities, primary care trusts and sexual health charities are increasingly turning to text services, apps and social media to provide advice and information to young people.

"It was increasingly becoming apparent that this is how young people wanted to talk to us," says Brook's Rachael Wyartt, who manages the Ask Brook web, text and phone services.

It makes sense to use the same technologies and social networks that teenagers use to communicate with friends and potential sexual partners, says sex education consultant Barbara Hastings-Asatourian: "This is such an effective and rapid way to share important stuff."

Text messaging services, many offering answers within minutes, are a key area of provision. The award-winning free Txtm8 service, provided by social enterprise Living Well, is used by the London boroughs of Enfield, Hammersmith & Fulham, Kensington and Chelsea, and Havering.

Local authorities around the country use similar systems. Brook's instant answer text service has been "incredibly successful" since its inception in 2009, says Wyartt, handling 2,000 queries in its first full year, and 5,000 the year after.

Web inquiry services, offering either instant replies or supplying a code that users can input to access their answer when it's ready, are also popular. The guaranteed confidentiality of such a system, with no need to enter an email address, is crucial to reassure potential users, says the Family Planning Association's helpline and information services manager, Lynn Hearton. "Actually writing down quite intimate stuff about your life is a very scary thing; sending it into the ether can make people quite anxious."

The organisation's Ask WES service, which began in 2009, provides answers within three working days, or immediately if the question is urgent. There has been a 46% increase in inquiries between its launch and the year to this April.

In the US, the Planned Parenthood Federation of America's (PPFA) live online chat service – targeted at young people aged 15 to 24, particularly those from the African-American and Latino communities – has held more than 65,000 conversations in its first 18 months. One in three users now access the organisation's website from a mobile device; last month it had nearly 1.2 million mobile visitors and nearly 73,000 visits to its Spanish-language mobile site, more than 17,000 of them from Mexico.

"We know that sex education can really make a difference in the decisions young people make — and now we can reach millions more young people with these new digital approaches," says Leslie Kantor, the PPFA's vice president of education.

Studies by the International Planned Parenthood Federation in Peru, Swaziland and Nepal on how to make young people's sexual health centres in the developing world more accessible have found that mobile technology has "immense potential" to draw young people in. "A number of member associations are now beginning to experiment with mobile technology," a spokesman says. "It's too early to provide any conclusive assessment, but early indications are that the approach has considerable potential."

One of the challenges of using such technology in developing countries is that even if the mobile market is booming, as in Africa, phone ownership among teenagers is not guaranteed.

But that doesn't mean the technology can't still be used to improve the quality and uptake of services. At the Liverpool School of Tropical Medicine, PhD student John Dusabe has developed an SMS system that will see informal village drug stores in the Mwanza region of Tanzania texting local health centres and dispensaries when young people come in seeking help. A unique passcode will then be sent back to the store owner for them to pass on to the client, who can present it to the dispensary to receive a confidential, fast-track service.

"Most of the people who man the drug shops don't have any medical training," Dusabe says. "What we want is for them to refer adolescents to the dispensary for professional treatment, instead of treating them without a prescription."

He's using text messages because they're more efficient than paperwork, which can get lost, and cheaper, in a country where notebooks can be costly. Shops are keen to get involved because those that do so are set to get licences to sell more drugs. The system will run for 18 months, being evaluated against a control.

Aside from offering advice, mobile technology can be also be used simply to direct young people to their nearest clinic or free condom service, after typing in their postcode, or allowing apps to use GPS to pinpoint the location of their phone.

In Kent, a new app for iPhone, Android and Blackberry works alongside the successful C Card service, which since 2007 has provided young people aged 19 or under access to free condoms given out by sexual health clinics, pharmacies, youth schemes and some school nurses. Now when they register for the scheme they are given a code they can scan to download the free app, which will direct them to the nearest participating outlet.

Around 46,000 teenagers in Kent have already registered for C Cards, which are used around the country. Jo Treharne, citizen engagement manager for NHS Kent and Medway, who came up with the app idea after realising that young people might not want to access information about condoms on home computers their parents might check, says other PCTs have approached her asking if they can use it.

Other apps are educational, often using games or quizzes to teach young people about risks and how to stay safe. One developed for Kent county council by student communications company Youth Media, and being used in schools, consists of a lottery game covering teenage pregnancy, STIs and the HPV vaccine. Since going live last June it has seen more than 23,000 views across 7,500 users.