It is when 18-year-old Blessing gets the bus home from school that the bullying starts. As she waits for the bus to draw out of the stop, a clique of angry-faced girls runs up to the window next to where she is sitting. They begin thumping on the glass with their fists. They scream abuse and call her names, saying that she is "dirty" and "disgusting". They throw chips at her, smearing the window with ketchup, treating her as if she is no better than a piece of rubbish.

Her classmates have just found out that Blessing is HIV positive, and this is a powerful scene from the new film Life in My Shoes which explores the reality of teenagers who live with the virus. The 30-minute feature was developed by Body & Soul, a ground-breaking charity that supports HIV-affected children, teens and families, and is set to be released next year as part of a high-profile campaign.

The initiative, which seeks to raise awareness of the stigma suffered by young people with HIV, is to be accompanied by a series of celebrity portraits by the photographer Rankin. So far his subjects include Kate Moss, the actor Ashley Walters and athletes Denise Lewis and Christine Ohuruogu.

"We are really trying to show that just because we are doing a campaign about HIV it doesn't need to be doom and gloom," says Rankin. "We wanted to capture a strong sense of warmth as well as have an impression of hope and life with bright and sexy images."

Working with Moss brings its own rewards. "It was great," he says. "I've known her for ages, but we are both so busy we only see each other from time to time. It's always amazing shooting her and catching up. We have a laugh!"

Beneath the celebrity gloss, there are serious issues at stake. Life in My Shoes is based on the experiences of teenagers who have the human immunodeficiency virus which, if left untreated, can lead to Aids. Many of the teens who shared their stories also took part in the production as actors, extras or members of the crew. In fact, the distressing scene on the bus where the fictional character of Blessing is hounded by her friends actually happened to a young woman living with HIV on a London housing estate – in the end, some of the abuse hurled at her was deemed too vicious to include in the final script.

"A lot of us have had similar experiences," says 22-year-old Isabella, an extra in the production, which was filmed over a fortnight in Hackney during the summer. "When I told one of my closest friends I had HIV, she started saying: 'Oh, you can't use this cup. You've put me in danger.' It does hurt because people think HIV is dirty or that you only get it if you're promiscuous or you're a poor person in Africa. It's not true. When I hear all those things, it really ticks me off. I think to myself: 'But that's not how I am.'"

Isabella's experience isn't unique. There are numerous incorrect cultural perceptions that still persist around HIV and Aids. Prime among these is the idea that it is an epidemic that belongs to the 1980s, a time when the UK government heightened the public's awareness by posting leaflets to every household in the country. In reality the disease has now been bequeathed to a new generation – around 11% of HIV infections are among babies who acquire the virus from their mothers, and although substantial medical advances have been made in recent years in managing the disease, there is still no ultimate cure.

And yet despite having been confronted by their mortality at such a young age, the majority of teenagers I meet at Body & Soul's headquarters in east London live happy and fulfilling lives, largely because the charity offers them a safe space in which to talk openly about their situation with other young people who understand exactly what they're going through.

"This place has really given me more confidence," says 16-year-old Lily, who was born with HIV. "It's a beautiful place where I feel really comfortable because I can say 'HIV' out loud. The rest of the time I feel like I have to speak in code. Like if I go on a school trip I've got to think of a way of explaining why I need to take medicine… But it doesn't feel like a weight I have to carry around. If anything, it pushes me more to do well."

Lily, who had a small speaking part in the film, is now determined to be an actress. "I like Will Smith and Cameron Diaz," she says, waving her hands expressively as she speaks, each fingernail painted brightly in a different colour. "Doing this was definitely a great experience."

For Tudor Payne, a commercial director who gave his time for free to direct Life in My Shoes, it was important to counterbalance all the "very dark images from films like Philadelphia and ads that showed people dying. The images that came out a few years ago were depressing, but when you meet the teens at Body & Soul, they're full of life, and we thought it was important to show that. We wanted to do something that challenged the stigma."

Ignorance is still a real problem. In 2009 a study conducted by the People Living with HIV Stigma Index found that 21% of the 867 participants had been verbally abused or harassed in the past 12 months because of their status; 12% had been physically assaulted. Last year a Body & Soul questionnaire of more than 500 12- to 18-year-olds found that despite increased awareness of HIV, there was a contradiction between their knowledge and their behaviour. So although 81% of respondents knew the virus could not be transmitted by sharing a cup, only 27% of them said they would actually be willing to drink from the same cup as a person they knew was HIV positive. Eleven per cent said they would not remain friends with someone who has the virus.

"If you told people you had cancer, you'd get sympathy and support," says Payne. "But if a teenager tells their friend they've got HIV, there's so much prejudice still around." It was for this reason that the decision was made to hold an open casting process for the film, whereby aspiring young actors were encouraged to learn a script and upload an audition online. "We made sure the script contained important facts about HIV and attitudes that challenged stigma," he explains. "This meant thousands of young people motivated by their desire to be famous learned the script and in doing so digested facts that they will probably remember for the rest of their lives, so already the education has begun."

Pearl Mahaga beat 700 other hopefuls to claim the lead role in Life in My Shoes.

More than 700 teenagers took part. The eventual winner, who played the part of Blessing onscreen, was 19-year-old Pearl Mahaga from Luton, now in her first year of a law degree at Cambridge University. "I really do believe that young people watching the film will feel more empowered," says Mahaga. "There's a lot of underlying emotion there, especially in the bus scene, and I hope that will roll down into normal conversations so that, if someone is making an inappropriate comment about HIV or Aids, they will have the courage and confidence to say: 'That's not OK.'"

The timing is crucial. In September a House of Lords committee estimated that almost 100,000 people in the UK will have HIV by 2012 and that efforts to stop the spread of the disease were "woefully inadequate". The actual numbers are likely to be far higher: some reports estimate that around a quarter of people with the virus are unaware they have it. Lord Fowler, the committee chairman, warned of the "potentially huge cost implications… of failing to deal effectively with the epidemic", and stressed that the government "should ensure that HIV and Aids is a key public health priority".

In this climate, the work of groups such as Body & Soul becomes increasingly urgent. The charity is one of the only organisations in the UK specifically designed to help entire families affected by the illness, promoting a holistic approach that provides youth groups, well-women clinics, yoga and therapy sessions as well as information services providing welfare and benefits advice. But their work is difficult to publicise – for obvious reasons, the people who go there want their identities protected. As a result, it is harder for the public to identify with their plight and put a face to the story.

Which is why the Rankin portraits are so important: if a high-profile celebrity is pictured promoting greater HIV and Aids awareness, the feeling that the disease is something shameful or frightening is instantly lessened.

"It's really important we remember that HIV does affect lots of people in the UK and that so many of these people are having to hide their status because of fear of discrimination," says Rankin, who asked each of his subjects to wear something yellow for the photographs – the trademark colour of the Life in My Shoes campaign. "But this campaign really has the capacity to change that and to bring attention to the fact that just because you are HIV positive doesn't mean you need to live a double life and fear how people will treat you."

Ashley Walters, who recently starred in the Channel 4 drama Top Boy, was one of those photographed. "The prejudice out there definitely needs to be tackled," he says when we speak. "When I was growing up, HIV and Aids was talked about a lot at school. I think today it's not being talked about enough.

"I grew up in southeast London and the last time I read any statistics, it said that that part of London had one of the highest rates of HIV and Aids among young black males. That really scared me. I have three kids, and with them growing up I'm really aware that they need to be educated about this."

Emily Head, who plays Carli D'Amato in the hugely successful sitcom The Inbetweeners, was another of Rankin's subjects and also helped with the audition process, offering to read the script with some of the hopefuls. "I wanted to do this because a lot of people still don't realise you can live a fairly normal life with HIV and you can't catch it by shaking hands with someone. I think the story of Life in My Shoes is really powerful: it's about a young girl struggling to overcome some of the things she faces through having HIV. It's a difficult place for a teenager to be."

Back at the Body & Soul offices, Lily is munching her way through a handful of M&Ms, recounting her experiences of filming on-set in a rapid stream of enthusiastic chatter. In between the excited reminiscences about improvised scenes and costume changes, she falls suddenly silent. When she resumes, her voice is slower, more considered. "It felt like the characters were speaking for me," she says. There is a thoughtful pause before she adds: "And it's great because their voices can be heard."

bodyandsoulcharity.org and lifeinmyshoes.org

• This correction was published on 18 December 2011:

"Body & Soul" (Observer Magazine,) said "around 11% of HIV infections are among babies who acquire the virus from their mothers". This was a global figure. We should clarify that in the UK, according to the Health Protection Agency, of all children born to HIV positive women (both diagnosed and undiagnosed) between 2006 and 2010, it is probable that around 2% became infected.