When Zoe Sugg, better known as YouTube superstar Zoella, released her first novel Girl Online in November, it scored the highest first-week sales for a debut author since records began, selling 78,109 copies in seven days. But as more people have read the book, some have begun to ask if it was written entirely by Zoe Sugg.

Today, a spokesperson for Penguin Random House told the Sunday Times that "to be factually accurate you would need to say Zoe Sugg did not write the book Girl Online on her own".

Later, Sugg posted a message on Twitter saying: "Of course I was going to have help from Penguin's editorial team in telling my story, which I talked about from the beginning.

"Everyone needs help when they try something new. The story and the characters of Girl Online are mine.

"I want to thank all of you who have taken time to support the book."

The publishers have signed a two-book deal with Sugg.

Speculation began because of 24-year-old Sugg's acknowledgements page in Girl Online, which reads: "I want to thank everyone at Penguin for helping me put together my first novel, especially Amy Alward and Siobhan Curham, who were with me every step of the way.”

Alward is Sugg's editor. Curham's exact role is unclear, but she usually works as a novelist and freelance writer of young adult fiction.

Some bloggers claimed to have found an archived, deleted post on Curham's website about being asked to write a novel in six weeks, which could in theory fit with the timeline from Zoella announcing her novel to its release.

Despite chronicling much of her life on social media and in her YouTube vlogs, Sugg rarely mentioned working on her novel, which is about a teenage girl whose blog goes viral after she meets a rock star, before publication.

This might answer some of your tweets! X pic.twitter.com/NCuC3VhxiG — Zoë (@ZozeeBo) December 7, 2014

Ghostwriting is a common feature of celebrity publishing. Former glamour model Katie Price makes no secret of the fact her novels were ghostwritten by Rebecca Farnworth, who died last week at the age of 49. Katie Price's novel Crystal, written by Farnworth, outsold the entire Booker Prize list the year it was published.

Actors, musicians, athletes and politicans work with ghostwriters as a matter of course. Sometimes they are credited - as in the case of Roy Keane's recent book with Roddy Doyle, or Alex Haley's co-authorship of the Autobiography of Malcolm X; at other times they are not. The authors of such ghostwritten books are people who are famous for something other than writing. Zoella has a following thanks to viewers of her video blog, not because she is the new Zadie Smith.

Very interesting to learn that a certain untouchable vlogger has had her debut novel ghostwritten. — London Beauty Queen (@LBQblog) December 2, 2014

im happy for zoella doing well for herself and all but having a novel ghostwritten for you and then slapping your name on it isn't cool — Zoë (@zoewithumlauts) December 4, 2014

I can't believe people are actually surprised about the fact that Zoella's novel is *probably* ghostwritten. Of course it is. — Sweet Hun (@EmilyHatzar) December 3, 2014

Inevitably, some people have asked if how much it actually matters that the book may be ghostwritten. As the Bibliodaze blog put it: "80,000 sales in one week speaks a hell of a lot louder than this kind of discussion, and many of Sugg’s fans will remain dedicated to their idol."

Plenty of popular novels, especially those aimed at children and young people, have been ghostwritten. Although Anne M Martin wrote many of the hugely popular The Baby-Sitters Club series of books published under her name, a number were ghostwritten by Peter Lerangis. Similarly, Francine Pascal's Sweet Valley books for teenagers were largely written by a range of ghostwriters.

On the back cover of Girl Online, Sugg is quoted as saying: "My dream has been to write a book, and I can't believe it's come true. Girl Online is my first novel and I'm so excited for you to read it." The biographical details on the book say that Sugg "has been writing stories ever since she was little".

The Telegraph's Anita Singh called Girl Online "sugary as a frosted cupcake... Even Winnie the Pooh might regard it as a bit twee".

Siobhan Curham could not be reached for comment.

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