Not going to lie, it was the Stephen King recommendation that made me wary. I've hated most of the King works I've read. Don't get me wrong, they're very well-written. I'm just not a fan of his stories.
That being said...Todd Travis is an author to have on your radar.

SEX, MARRY, KILL.
An online game that would change their lives and give them power over others. They could do anything they wanted, sleep with anyone they wanted to, kill anyone who got in their way. Their every fantasy fulfilled. But at a mortal price. They soon discover that game will consume and destroy them unless they find some way to stop it before it’s too late.
Most of the reviews are in the same vein. It's very well written and holds just the right amount of terror.
I definitely recommend clicking here and getting your own copy.

Special Agent EMMA KANE, a former DC cop and damaged goods now with the FBI, is assigned to baby-sit burned out profiler JACOB THORNE, once the best in the business but now said to have lost his edge, as they both fly to Nebraska to catch this maniac.
Thorne is erratic, abrasive and unpredictably brilliant, but what he and Kane find in the heartland is much more than anyone bargained for, especially when the Iceman challenges them personally, where it hurts most.
The clock is ticking and a little girl’s life is on the line.
And maybe even more with that, once they find out what he’s really up to.
I literally just finished this book (like, just clicked through the last page)
Oh my God.
Sonofabitch.
Freaking awesome. More than one WTF Moment I didn't see coming. Travis is definitely a writer to watch.
In fact, click right here and start reading ASAP so we can suffer together.