If you go down to the tweets tomorrow, you're sure of a big surprise… for here lurk goblins and werewolves and Sheela Na Gigs, and all manner of strange beasties and stories lost to the mists of time, legend and myth. Because, while Twitter might be an utterly 21st-century affair, it's also home to a growing number of people who, under the hashtag #FolkloreThursday, are getting back to their roots and using the social network to reconnect with traditions, some of which are long forgotten.

Behind the hashtag – and the Twitter account @FolklorThur – are three friends who met on the internet and have been amazed at the way their weekly informal discussions about their shared interest have spiralled into an online phenomenon. The trio behind #FolkloreThursday are Dee Dee Chainey, Willow Winsham and Seline Stevenson. Dee Dee has a background in archaeology, Willow is a witchcraft historian, Seline a folklore enthusiast. Dee Dee says, “It all started with a tweet about the Efteling fairy tale theme park in the Netherlands; we joked about how we should head off on a trip right away and that's pretty much how we started chatting about our shared love of folklore.

“We had been talking for a while about the need for a central 'go to' place for people to find all things folklore related on the net, and again it was a case of a throwaway comment that got us seriously thinking about the need for a hashtag day specifically for the folklore crowd – there wasn't one, and so we decided to create our own.”

On any given Thursday, the tweets are a mine of information. A handful of examples from last week sees @MirthandMisery tweeting about a Welsh hobby horse with a real equine skull; @SmithsonianFolk talking about Japanese dolls set adrift on the sea to take bad spirits away and @TheGhastling issuing a warning about waking a sleeping person, lest they die while their soul is away from their body.

Anyone can, and does, participate and are some pretty big names get involved, too. Last week, for example, the film director Guillermo del Toro, whose 2006 movie Pan's Labyrinth drips with Spanish folklorica, dropped in.

“The most humbling aspect of running #FolkloreThursday has to be the privilege of seeing the community and the people within it grow as the weeks go on,” says Dee Dee. We've had a lot of people find us who have been initially tentative when it comes to posting, and are now debating and sharing as if #Folklore-Thursday is their second home.“

A lot of folklorish knowledge is out there already, Dee Dee concedes. Nonetheless, she claims to be curating material that is forgotten or at risk of disappearing altogether. “Folklore, traditionally, is an oral thing,” she says. “It's only in recent years that people have started studying and documenting it on a wide scale. A lot of sources are locked away in university libraries, or in journals that are quite expensive to access. Reading other people's blog posts is often a great way to get an overview of a subject without having to dig through piles of papers that might be in a different city, or might be unavailable altogether.”

Generally trending for several hours each day, the hashtag grows with popularity every week and now there's a freshly launched website (folklorethursday.com) which brings all the tweeted knowledge into one place. It makes for fascinating – if sometimes grim – reading, with articles on the myth of Charon, the ferryman across the River Styx, the church in Milan built with the bones of the dead, and Cruel Coppinger, one of the most fearsome of the Cornish smugglers.

So why Thursday, anyway? Any particularly folklorish reason? Not initially, says Dee Dee. “Someone was already using #FolkloreFriday as a personal hashtag, and we didn't want to step on toes. But funnily enough, once we got going, one of our regulars did tweet about why Thursdays are particularly suitable, being the most significant day in Norwegian traditions.” Ah, the old wisdom…