Here's some links for some similar online writers. I suspect most of these might already be familiar. Feel free to add any I've missed in the comments.
I'll start with the general:
Biggest sex stories site on the web? They have everything. My stories lurk in the Erotic Horror section. They also have Non-human and Sci-Fi & Fantasy categories for people that like happier endings. I usually check either the Last 30 days Top list for horror or enter "Succubus" into the story search every so often to see if anything interesting popped up. The quality is as you'd expect for an amateur writers site, but there are some gems to be found.
Monster Girls galore. They have a fanfic section with lots of stories in progress. Kenkou Cross's Monster Girl Encyclopedia is the primary influence despite my best efforts to hijack the forum to my own nefarious purposes. A place to go if you like stories where the girl doesn't end up killing the boy at the end.
And for those of you that prefer Girl eats Boy, there's Eka's Portal. It's predominantly a Vore site, but there's a slight overlap for lovers of sexy, predatory females. Some of my stories (Flesh Pitchers of Prague, Wrapdance) fall into this overlap and I post them up there every so often. There's other writers/artists tackling similar themes. 4ofSwords(used to be ohida) runs a regular writing group thread I keep meaning to submit stories to, but never get around to doing.
Lost Boy's Other-Worldly Story Links
Quite possibly dead. Updates very rarely nowadays. It does have a fantastic collection of good stories. This was the first place I blundered into when searching for succubus fiction on the net.
And the writers:
The first writer I stumbled upon, so it's all his fault. His Castlevania fanfic got the idea of a succubus perfectly I thought. She kills through sex and in a way that feels more concrete and realistic than a nebulous energy/spirit/soul/aura drain. Both his Lustful Summoning and Succubus Ranch series are highly recommended. He's been a little quiet of late, so go prod him.
It's Always Time is a great goo (slime) girl story that features a fairly clever plot alongside all the messy sex. I haven't heard much of him of late, but if he's still out there he should probably stick the story up on amazon and make some money from it (hint hint).
Likes a sexy female pred. Ranges from vamps to full-on vore. Damn good artist as well.
Boobs! Gigantic Boobs! Boobs of the apocalypse! Always fun.
Some good fantastic femdom-y succubus-y type stories. Also needs prodding.
Borrowed Verde's garden and filled it with some fascinating creations.
There's others I've undoubtably missed or not got round to finishing yet such as Galloglaich's Cemetery Summons series and bashfullyshameless's Angels, Demons and Alex series (nominated in Literotica's sadly pointless and horribly abused end of year awards). As well as others I'm too tired to remember as yet another blog post has ballooned into a huge essay. Feel free to mention any I've missed in the comments. I'm always on the lookout for new and interesting succubus stories.