As the clock ticks down to the March 19 release of Clockwork Princess, the third and final book in Cassandra Clare’s bestselling The Infernal Devices series, Simon & Schuster Children’s Publishing has some innovative marketing plans in place for the novel’s launch. One highlight of the campaign was the February 26 online chapter reveal, which YA readers controlled as they collectively tweeted the hashtag #ClockworkPrincess, unlocking the opening chapter word-by-word and enabling fans all over the world to read it simultaneously in real time. And there were lots of them: more than 560,000 tweets were sent in 27 hours, and the hashtag became a top trending topic on Twitter all over the world, including in the U.S., Spain, Italy, Guatemala, Singapore, and the U.K.

The enthusiastic international response to the Twitter chapter reveal campaign comes as little surprise. Clare’s novels have been translated into 35 languages, and The Mortal Instruments series (which first introduced the Shadowhunters – half-human, half-angel demon fighters), has 16 million copies in print worldwide. The Infernal Devices, a prequel series set in Victorian London, has a global in-print tally of six million copies. There’s a one million-copy first printing on order for Clockwork Princess, which will be published by Margaret K. McElderry Books and is embargoed until its pub date.

The chapter reveal, now available on the Shadowhunters Web site, followed the model of the publisher’s fan-driven cover reveal for Clockwork Princess, which generated 30,000 tweets within two hours to expose, bit by bit, the book’s cover. “We are always trying to bring something new to the table while promoting Cassie’s books,” says Anne Zafian, v-p and deputy publisher of S&S Children’s Publishing. “Since she has such good online outreach and social networking skills, it was great that, with the Twitter campaign, the first chapter could be revealed worldwide at one time.”

Clare says she was “thrilled” by her fans’ enthusiastic response to the chapter reveal – and at the Twitter campaign’s scope. “I was really pleased that all my readers could participate,” she says. “And because there’s often such a long gap often between finishing a book and having it released, where you wait in anticipation to see how it’s received, it was great to be able to watch people react in real-time as they read. Because of social networking, I could see readers chatting with each other, sharing theories and pictures. It really made me think about how much reading as a group activity has grown on the Internet.”

Additional marketing efforts to build pre-pub Clockwork Princess buzz included the early February launch of the Cassandra Clare’s Shadowhunters app for Apple and Android, which offers a look at the novel’s prologue; and the February 21 debut of the book trailer on EW.com’s Shelf Life blog. For retailers, S&S created “pre-order now” easels and floor displays; TV ads for the novel will air on the Dish network after pub date.

On March 19, Clare will embark on a weeklong, eight-market tour, traveling in a wrapped bus decorated with book covers and a poster promoting the movie The Mortal Instruments: City of Bones, which opens in August. She’s looking forward to her first-ever bus tour for several reasons. “I have to admit, I hate flying,” she says, “but I think the real core idea of the bus tour is that there’s something about the on-the-ground nature of it that really builds excitement. The wrapped bus is a cross-country billboard for both the book series and the upcoming movie.” She also likes the fact that she can carry more giveaways for fans, since she’s not flying. “Plus, it makes me feel like I’m in a rock band, writing songs on the road. I’m tone-deaf, but it’s nice to dream!”

Though the author says it isn’t easy to bid farewell to The Infernal Devices series – “I am sad, very sad. I have grown to love the characters like family” – she welcomes the next chapter of her career. “Fortunately, I have much to work on and look forward to,” she says. “There are the Bane Chronicles, a series of e-novellas that I’m co-writing with Maureen Johnson and Sarah Rees Brennan, releasing starting this April; The Shadowhunter’s Codex [October 2013]; City of Heavenly Fire, the conclusion to The Mortal Instruments [March 2014]; and a brand-new series, The Dark Artifices [2015], which is going to bring me a whole new generation of Shadowhunters to write about.”

Clockwork Princess by Cassandra Clare. McElderry, $19.99 Mar. ISBN 978-1-4169-7590-8