DeathWeb (Fox Meridian, #3)

A serial killer has murdered eleven people over the last four years, the link between the crimes unnoticed until Fox Meridian's AI personal assistant, Kit, makes the connection. The only thing which seems to connect the victims is LifeFit, a plug-in application which allows users to find virtual exercise companions over the most popular social network in the world, LifeWeb. All the victims vanished while out running, their bodies turning up days later. Every one of them has been tortured to death. The killer is back in New York after visiting Cape Town and Berlin, and the bodies are piling up.
But as the investigation stalls with no clues to the mad man's identity, Fox finds herself called upon by her estranged parents who want her to find a missing teenage girl who may have been kidnapped and taken into the wastelands of the Southern Protectorate.

I'm a computer programmer who has been writing fantasy and sci-fi since I was fifteen. The Thaumatology series is, therefore, the culmination of 30 years work! Wow! Never thought of it like that.