When I first set up a website to collate women's routine experiences of prejudice and harassment, I didn't expect to receive so many horror stories – nor so much hate mail

When I started the Everyday Sexism Project a year ago, I never imagined that by now it would have attracted some 25,000 entries and be about to spread to 15 countries. Nor even that I'd be writing about it in the Guardian – or that this would be the latest in a chain of articles that has encompassed the Times of India, Gulf News, Grazia South Africa, the Toronto Standard, French Glamour and the LA Times.

When the project was launched, with no funding or publicity, I thought it might provide a talking point for my friends and hoped that some of them might have stories to share. I hoped to gather 100 women's stories, if I was lucky. Instead, it spread like wildfire, as more and more women began to add their experiences – women of all ages and backgrounds, from all over the world. A seven-year-old disabled girl and a 74-year-old wheelchair user recorded almost identical experiences of shouted jibes about "female drivers". A video-shop cashier, a midwife and a marketing consultant suffered indistinguishable experiences of sexual assault by senior male colleagues.

A schoolgirl and a widow reported being pressured and pestered for sex. A reverend in the Church of England was repeatedly asked if there was a man available to perform the wedding or funeral service: "nothing personal". A man was congratulated for "babysitting" his own children. A 14-year-old schoolgirl wrote: "I am constantly told I can't be good at things because I'm a girl. That I need to get back in the kitchen. That all I'm good for is cleaning, cooking, and blowjobs." A DJ explained how constant harassment and groping had made her dread the job she once loved.

A girl in Pakistan described hiding sexual abuse for the sake of "family honour". A woman in Brazil was harassed by three men who tried to drag her into their car when she ignored them. In Germany, a woman had her crotch and bottom groped so frequently she described it as "the norm". In Mexico, a university student was told by her professor: "Calladita te ves mas bonita" (you look prettier when you shut up). In Israel, a teacher with a master's degree who speaks six languages was told she "wasn't a good enough homemaker for my future husband". In France, a man exposed himself to 12- and 16-year-old sisters as they tried to picnic in a public park. On a bus in India, a woman was too afraid to report the man pressing his erect penis into her back.

Every time the project was featured in the foreign press, I would receive emails from women in those countries asking if they could start a version of the project there because it was desperately needed. Women in the US, Canada, Australia, South Africa, New Zealand, Russia, Italy, the Netherlands, Portugal, Brazil, Spain, Argentina, Germany, Austria and France have all volunteered to moderate the local content. We hope to make a great collective resource where we'll be able to compare trends from different countries. In some ways we already can.

One woman was sexually assaulted on a transatlantic flight, another by the postman on her doorstep, another in a bookshop, aged 16. In a Twitter discussion, when the subject of sexual assault on public transport arose, somebody wondered whether it had ever happened on a tram. I searched the database. There were 25 entries.

Some days, it was very hard to keep reading. Without any funding, it became increasingly difficult to juggle the website administration and social media accounts with increasing requests to share project data with MPs and trade unions, and speak at universities and schools.

And the huge success of the project wasn't the only thing I didn't anticipate. One of the earliest entries read: "You experience sexism because women are inferior in every single way to men. The only reason you have been put on this planet is so we can fuck you." The message ended: "Please die." The sheer level of vitriol took me by surprise, as hate-filled missives poured in, ranging from graphic descriptions of domestic violence to threats of torture, death and rape.

But as the threats worsened, I discovered the most incredible support network. Anyone who describes feminism as an in-fighting, back-biting movement has clearly never been as lucky as I was, at those lowest moments, to discover in it the strength and kindness, advice and support of so many other women and men. A team of around eight volunteers helps collate the entries – about 1,000 a week – collecting together the ones that come in via Twitter and through the website. They are coordinated by Emer O'Toole, who rounded up a group of feminist volunteers and has been organising them on a rota system ever since.

Success stories began to pour in. In their own ways, women started to fight back. One runner, sick of catcalls and wolf whistles, started making her own "honk if you love feminism" T-shirts. A woman tired of cold-callers asking to speak to "the man of the house" started putting them on to her six-year-old son, who'd sing: "I'm sexy and I know it." A football fan wrote to the chairman of his club to ask why the fans were singing such misogynistic chants. And email after email started arriving from women who had found the strength to report harassment, stalking and sexual assault to the police.

This time last year, I had an idea. Today, 25,000 women's voices have turned it into so much more.

Visit the Everyday Sexism Project at everydaysexism.com Tweet @EverydaySexism