I'm trying to remember a book I picked up around 2014, the copy seemed reasonably worn but it could have been recent. The story centred on a teenage boy who spent all his time in a worldwide VR MMORPG.
From what I remember of the virtual world, it was a standard (Tolkein-style) fantasy setting. I think he was on some sort of quest that had repercussions in the real world. It mentioned that the only time he spent out of his VR chair was to do an intensive exercise regime in the morning because keeping fit helped the sharpness of your mind, and he looked down on people who didn't bother.
There was also a high-school girl, who received a mysterious invitation to be a part of some covert group in the virtual world who were hunting down people like the boy to stop them from completing the quest. Her potential group is a small cell of ~5 people. She may have had to recruit other people from her school, or was head-hunted specifically because she was a high-schooler? Finding out the nature of the secret group was a story arc, and not explained right away. It covers some high-school drama about her peers, mostly via chat and email.
I remember that she logs on to her "desktop" which is a grand room like a domed observatory with planets visible in the background. It takes some time to explain the concept of a desktop as a facade for your filing system, and says that some people have actual filing cabinets in theirs because they can only think literally about it (which leads me to believe it was written before the 2000's, when everyone wasn't as familiar with computers).
The feel of the writing was cheesy and 90's, with the covert group being called something like "net detectives". I read it in English in New Zealand. I only read half of it, so it would be great to find out what it was.