Best-selling German author Sarah Sprinz's series of young adult books has received a boost from an unlikely quarter: a community of literary enthusiasts on social media platform TikTok.

The #BookTok trend has exploded in recent times, with a growing number of readers posting reviews and engaging with writers, while authors use it to promote their works.

To some, it seems counter-intuitive -- a platform known for short and often light-hearted videos is not the obvious place to encourage an activity like reading that requires deep concentration.

But videos with the hashtag have racked up billions of views, and helped to propel the popularity of some works, while bookshops are rushing to set up stands where creators can film videos.

The trend "is super important for me", Sprinz -- author of the hit "Dunbridge Academy" series, set in a boarding school in Scotland -- told AFP in an interview at the Frankfurt book fair.

"Personally for me, I believe it played a role (in my success), because I have seen a lot of videos recommending my books."

The trend, which often sees creators post emotionally charged reviews of books, has been particularly effective in attracting a new audience of younger readers, said Sprinz.

"I think it is nice that through TikTok, a completely new, younger target audience is becoming aware of reading," said the 26-year-old.

- 'Impact on book sales' -

According to TikTok -- which is owned by Chinese company ByteDance -- #BookTok has received more than 84 billion video views to date on the platform, and successful genres include romance and fantasy.

"#BookTok has become the place for book recommendations and discovery as well as for sharing reviews and tapping into fan culture," said Tobias Henning, general manager, TikTok Germany and Central and Eastern Europe.

It is also "having a real world impact on book sales globally", he added.

One success credited to #BookTok is that of US author Colleen Hoover's novel "It Ends With Us", which saw sales soar after it gained traction in the community.

A typical review shows a woman sobbing as she reads the novel, with music playing and a voiceover reading, "I've never cried for so long after a book."

With the clout of #BookTok growing, the annual Frankfurt fair, the world's biggest publishing event, has made TikTok a partner for the first time.

Several creators and enthusiasts are also in attendance.

"I mostly do (Tiktok) content about books, mostly about novels, and I try to upload two videos a week," TikTok user Sofia Reinbold, who came to the fair after reading about it on the platform, told AFP.

The 17-year-old added she had received "feedback from people who have bought books after watching my videos".

- 'Multiplier' effect -

For Sprinz, the #BookTok phenomenon is driven by the fact that TikTok is a visual platform, allowing people to show how they feel about a book.

And people being stuck at home during the coronavirus pandemic may have accelerated the trend.

"A lot of people perhaps felt a bit lonely and isolated," she said, adding it was a good platform "to network again and find common hobbies like reading".

She also downplayed the suggestion there was somehow a contradiction between spending more time on social media and trying to promote literature, noting that people read in different ways nowadays, including on e-books and smartphones.

But social media alone "cannot make a successful book", she said.

"TikTok and #BookTok are a kind of multiplier, and a good opportunity to pass on recommendations for books."

But "there must be more to it," she said. "The book must of course be good."