Oline Cogdill
Back in 1991, Paul Levine's novel Night Vision followed attorney Jake Lassiter who was caught up in the murder investigation of three women who belonged to Compu-Mate, an electronic network whose members talk dirty to one another.
Back in 1994, Julie Smith wrote about a loosely connected group who had an active virtual life on TOWN, a computer bulletin board. That novel, New Orleans Beat, followed Smith's New Orleans detective Skip Langdon investigating what seems to be the accidental death of a man who fell off a ladder at home. The investigation takes a turn when Skip learns that members of TOWN suspect their friend was murdered because he had recently posted about flashbacks to his father's death 25 years before.
Back then, when I reviewed these two novels, the idea of an online community seemed as remote to me as, well, the idea that everyone would carry cell phones.

The internet was a tool I barely was aware of. I didn't even have my own computer then. I would never have thought my work, my friends, my spare time would be consumed by the Internet. I didn't have any idea of the power the Internet would have.
But mystery writers certainly were aware of the Internet's power. Now, so many authors are using the Internet as a major part of their plots.
Here's just a few I've come across recently:
J.A. Jance's latest Ali Reynolds mystery, Fatal Error, concerns man who meets and proposes to women over the Internet. The problem is that he's juggling several women at a time, one of whom may have snapped and killed him. Jance has said that Fatal Error was inspired by one of her friends, who thought she had a serious relationship with a man she “met” online, but then found out he was carrying on in a similar fashion with countless other women.
Daniel Palmer's Delirious revolves around Charlie Giles, the inventor of a new digital-entertainment system for automobiles. Charlie's life unravels when compromising emails and web sites are found on his company computer. A sophisticated hacker is out to destroy him.

In April, Hallie Ephron will publish Come and Find Me in which a young woman retreats to her virtual life following the death of her husband. Unable to cope with the world, she lives in her own world online.