Online-chat clown crosses over to reality, commits murder

Question

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).

Answer 1

Terminal Games by Cole Perriman (Cole Perriman is actual a husband and wife team Pat Perrin and Wim Coleman).

The clown is Auggie rather than Augie. The intro says:

We wrote Terminal Games under the pseudonym Cole Perriman, and it was first published in 1994. At that time, New York publishers were just discovering fax machines. Most people hadn’t used email, and “Internet” wasn’t yet a household word. There was no Google, Facebook, The Sims, Twitter, Amazon, WiFi, texting, or … well, you get the picture.

So as you say it predated the Internet, at least in its modern form.

There are lots of excerpts I could cite, but let me choose just one covering your mention of the clock striking thirteen:

Marianne felt that pang of pity again. If Auggie was true to his word, he would put an end to his life in the next few minutes.
If he is true to his word …
She shuddered again at the thought of her own broken promises. Would Maisie keep the network turned on? Would Auggie, the ultimate trickster, be true to his word?

For the moment, there was nothing else to say. Marianne stared at her computer clock and waited. Time slowed considerably during this last handful of minutes. Then, at long last, five o’clock had come. Marianne felt a terrible anticipation. Now Auggie was experiencing a time of day he never knew existed—standing face to face with the simple fact of his own nothingness. Now he understood. He simply had to.
The clock has struck thirteen