YA book with secret chapters online

My daughter recently talked to a girl and they shared their favorite books. But she forgot title and author. This is what I know:
- it's probably a YA book, although I'm not sure
- after the book was published, some secret chapters were published online
- the author has published parts of his book als street-art on random places, there are loads of fans who are continually searching for these parts

That's all. Anyone got any clues? Thanks in advance!

The reason we need to know now, is that my daughter and I go book hunting in London this weekend, and she wants to buy this book....

Without even a hint at what the book is about, there's really nothing to go on here. Please share anything she remembers about what takes place in the story, who the characters are, etc.

You say "his", are you certain the author was male? That's at least a tiny tidbit.

I wish there was more. I know it's a long shot... The girls just talked about this being her favorite book and these were the elements they talked about. I'll check it just to be sure. Thanks so far! I'll get back with more information (I hope)

Sounds fascinating! Lots of clever sleuths here, I hope someone identifies it. Another useful piece of info would be if the 'street art' is in London? (Or even in UK?) and if it was a recently published book?

Among Us?

Found it by googling for:
book "alternate reality game" "secret chapters"

EDIT: This is a trilogy, starting with Doubt. On the website, they offer to send a free ebook.

>6 hnau:, that site knows a thing or two about flashy marketing, that's for sure.

Thanks for all the hints! But the book we were looking for was The Raw Shark Texts by Steven Hall. We accidentaly found it outside a bookshop on Charing Cross Road, in the clearance boxes - 5 books for 4 pounds :-) And there it was, brand-new as it appeared. Which fits with the theme of the book, I guess... Another great bookstory.

Touchstone: The Raw Shark Texts