With an active presence on Tumblr, 81,000 Facebook fans, more than 50,000 followers on Twitter, and a popular blog, bestselling YA author Cassandra Clare has built a robust fan base online since her first novel, City of Bones, launched The Mortal Instruments series in 2007. Originally conceived as a trilogy, the urban fantasy series will add its fifth installment, City of Lost Souls, next May. And on December 6, Margaret K. McElderry Books will publish Clockwork Prince: Collector’s First Edition, the second installment (after Clockwork Angel) of The Infernal Devices, a prequel series set in Victorian London—150 years before The Mortal Instruments takes place. Pre-publication online buzz about this novel grew louder this week, when the publisher debuted its book trailer on EW.com.

In its first two days online, the Clockwork Prince trailer garnered 2300 Facebook shares and an additional 2000 fans hit the "like" button, reports Anne Zafian, deputy publisher at McElderry. Senior marketing manager Elke Villa, whose team worked closely with Dirty Robber, the company that produced the trailer, notes that it has "the highest production value of any trailer we’ve done for any of Cassandra’s books," and cites an 'added bonus" to the video: a voiceover by actor Ed Westwick of Gossip Girl fame. "Westwick also narrated the audiobook of City of Fallen Angels and the forthcoming audiobook of Clockwork Prince," adds Villa, "but this is the first time we’ve used the voice of such a well-known actor on one of Cassandra’s book trailers."

Zafian predicts that the trailer’s release will lead to a spike in preorders for Clockwork Prince, which has a 750,000-copy initial printing. This is the largest first run to date for one of Clare’s novels, which have been published in 30 languages and have more than 5.5 million copies in print in North America alone (including e-book editions).

McElderry editorial director Karen Wojtyla, who is Clare’s editor, emphasizes the effectiveness of the author’s online outreach to fans. 'Cassandra is the most active writer online I have ever worked with,' she observes. "She loves her fans and communicates with them through every kind of connection available to her. She always talks to them about her next book, and she gets a huge number of preorders and sells a fair amount of e-books. It takes a lot of work and effort to have such a strong online outreach, but the teen world really responds."

Clare says that she finds online networking with fans "really meaningful." She adds, "I go wherever the social media seems to be going at the moment. It’s really about the importance of building a relationship with my readers, and it is a wonderful way to get the word out about my books and sharing news."

In fact, the decision to release Clockwork Prince’s entire initial print run as a collector’s edition with extra content, says Clare, "grew out of the online relationship I have with my fans. I’ve always offered them extra bits and pieces online, kind of like director’s cuts in movies—things like deleted scenes or scenes rewritten from another perspective or family trees—and they’ve always been met with great enthusiasm. So I thought doing an edition with added content would be a way to reward my loyal readers who buy the book when it first comes out."

In addition to the book trailer, the publisher’s marketing campaign for Clockwork Prince includes 30-second ads on MTV, scheduled to run during the first two weeks of January. Clare pre-signed 2000 copies of the novel, which are available to booksellers in 10-copy prepacks. "This is our way to reach out to the indie market," says Zafian, "and Cassie was a very willing partner in that."

On December 6, Clare embarks on a six-city tour to promote Clockwork Prince, which will give her some actual face time with fans. "That personal contact is irreplaceable," she says. "It’s wonderful to make online relationships, but meeting readers in person and hearing their stories is amazing. One of the great things about touring is the fans who come up to get a book signed and drop off letters to me. I have a great collection of them. They give me a chance to hear from people who aren’t online and to learn what my books have meant to them."

The Infernal Devices, Book Two: Clockwork Prince: Collector’s First Edition by Cassandra Clare. Simon & Schuster/McElderry, $19.99 Dec. ISBN 978-1-4169-7588-5