Zoella: vlogger tipped to top the Christmas book chart She inspires extraordinary devotion among her fans, with young girls regarding her as a big sister and teenage girls wishing she was their best friend. Spotting Zoella's ability to tap into the teen demographic, publishers fought to snap her up. Zoella signed a two-book deal with Penguin and the first of these, a debut novel called Girl Online, is predicted to be the year's fastest-seller when it is released on November 25 just in time for the Christmas market. The story of a teenage girl who writes a blog about school, boys and her "mad" family is being published in 15 languages and is in Amazon's top five best-selling children's books on the strength of pre-orders alone. Zoella has this huge fan base. Girl Online will be the fastest-selling children's book of the year, and I don't see why it won't challenge for the overall best-seller," said Melissa Cox, children's buyer at Waterstones. The book chain got a taste of the YouTubers" popularity when they hosted a recent signing for Alfie Deyes, Zoella's boyfriend and a fellow "vlogger" (short for "video blogger"). Police had to be drafted in to marshall the 8,000-strong crowd. Cox said: "We knew Alfie's book would be popular but we weren't anticipating these thousands of teenage girls turning up. "It showed that the YouTubers" moment has arrived. In the last couple of months, things have gone crazy for them. Zoella also has her own make-up line at Superdrug and is a target for brands desperate to use her in their advertising or tie her in to a sponsorship deal. She claims to turn down "90 per cent of all the deals that come in." The daughter of a businessman and a beautician, Zoella gained 3 A's at A-level and began an apprenticeship in interior design after leaving school. But in 2009 she discovered blogging, and it was a short leap to making her first online video. Her quirky, approachable style quickly won her a legion of fans. And while the overtly sexual performances of today's pop stars send chills down the spine of many a parent - Rihanna and Miley Cyrus being the main offenders - Zoella is a reassuringly clean-cut role model, who doesn't drink and is so anti-drugs that she doesn't even touch paracetamol. Her brother and friends are also vloggers, feted like Hollywood stars wherever they go. In addition to her YouTube subscribers, Zoella has 3.5 million followers on Instagram and 2.5 million on Twitter. She is determined to use her celebrity for good, helping young followers to navigate through the tricky teenage years. Her online "Anxiety Q&A" - she suffers from panic attacks - has been viewed over two million times. Her debut novel also addresses the issue of mental health. I wanted to inject something into the main character that would help people. As a 14-year-old with anxiety, to have read about that in a book would have helped me so much," she explained. Zoella readily admits that becoming a novelist hasn't been easy. "A lot of people have said it's loosely based on me, which is quite funny because it isn't," she said. I had help with editors, thank goodness, otherwise I'm not sure how it would have been. If proof were needed that the online world need not belong entirely to Zoella's demographic, her grandfather is also on Instagram, the photo-sharing site. He has more than 25,000 followers.