Part of a series of celebrations planned to mark 125 years since the birth of the British crime writer Agatha Christie, an online campaign is inviting fans to share their stories about the author via social media.

Christie's grandson, Mathew Prichard, has shared a handful of previously unseen letters sent from the author's fans and from Christie to her fans, including examples from fellow writer P.G. Wodehouse and from a WWII labour camp survivor.

The newly opened online portal "125 Stories" calls on fans to share anecdotes, with a selection of submissions to be exhibited alongside the fans' letters during the International Agatha Christie Festival, taking place September 11-19 at Torre Abbey in Christie's birthplace of Torquay, Devon, UK.

P.G. Wodehouse wrote in his letter than he was "pleased and proud" that Christie's "Hallowe'en Party" had been dedicated to him, and praised the title, writing "getting a satisfactory title is the most difficult problem."

A woman who spent a decade in a Romanian prison wrote in 1963 that she "was able to repeat to my cell-mates practically verbatim all of your works that I had read."

In 1959, a woman sent to a German labour camp during World War II wrote of a Polish translation of Christie's "The Man in the Brown Suit": "I read and re-read so often that I almost knew it by heart. The first few pages were missing so I didn't know the title or the author but for seven months it was my only link with a normal world."

The BBC is also planning to mark the anniversary year with new adaptations of "Partners in Crime" and "And Then There Were None."

Agatha Christie is the best-selling novelist of all time, having written more than 80 crime novels and short story collections as well as 19 plays and six novels under the name Mary Westmacott.

Her play "The Mousetrap" opened in 1952 and is the longest-running play in history.

Visit www.125stories.com to see the fan letters and to contribute a submission; it's also possible to submit via social media channels using the hashtag #125stories.