I read this story "post-internet"; that is, internet access and things like public chat networks were common and more-or-less routine, though mostly text-based rather than graphical - think IRC and MUDs, rather than Second Life.
The plot has the protagonist being a participant in an online service (online for only a few hours each night) where in addition to 'themed chats' with pixel/cartoon avatars and scenery, it was possible to compose and 'broadcast' animations (in the same style) - remember, this was more-or-less Before YouTube. One popular producer of these animations is a clown, identified as "Augie", whose animations are 'snuff' sequences. The protagonist becomes aware that the 'snuffs' match actual murders, and it becomes more-or-less personal when a close friend of hers is the subject of one of the murders.
In the end, it turns out that "Augie" is a sort of "gestalt overconsciousness" of many of the online service's users, housed in the service's computers somehow, and becomes aware that the protagonist is on 'his' track; the climax has the protagonist defeat "Augie" in part by proving that there is more to the world than the service (by having the service stay on-line for a few minutes past its normal shutdown, thus 'making the clock strike thirteen'). The protagonist is subsequently attacked by the gestalt 'taking over' real people - the same way the murders were committed - and manages to defeat "Augie" once and for all (though I don't recall those details).