I'm looking for fics that have Buffy in a demon world and have Spike either being there already, going to rescue her or heck keep her in that place with him. Just want demons to be the masters of the world. Plus for making humans slaves or second class citizens.

There was one that I read but I can't remember it sadly. Buffy was taken in by Darla when she was young. They knew she was a potential slayer. Then they gave her to a demon lord of a demon world as a tribute. She becomes a slave and part of the demon's harem only later to be offered up as a prize in a fight.

Prize of the Harem by DramaQueenLucy

Possession by icemink
Demon Seed by BuffyMeetsSpike

I think this would fit what you want in a way.
http://www.sinister-attraction.net/stories/a/prophecy.htm

Prophecy of Two, The
~ Author: Amanda K

Summary: In a world where vampires rule, Buffy finds herself powerless. Her single ally is Spike. Can she trust him to help her find their way home?

Here are the links to the other fics.

http://spikeluver.com/SpuffyRealm/viewstory.php?sid=17125

Summary: Response to BSV challenge 157. AR When Spike loses in a high stakes poker game he ends up in a demon slave market, where a mysterious human girl purchases him.

http://bloodshedverse.com/stories.php?go=chapters&no=12604

Goes AU after Life Serial. After Buffy is kidnapped by a horde of demons, Spike comes to her aid, only to find her imprisonment was worse than he could have imagined.

A Different Light by Dreamweaver

Summary: During the fight over the Gem of Amara, Buffy and Spike get pulled into another dimension.

Running Wild by Dreamweaver

Summary: In order to help Glory, Doc sets out to get rid of Buffy and the Scoobies just after "Into The Woods" and co-opts Spike to kill her.

To the Victor by Maryperk

Summary: Based on Buffy's dream from Day 8 of Fixing the Factors, in fact that's the prologue. Spuffy of course, with other pairings, canon and otherwise. Angelus has been away from the clan for many decades. When he comes home he finds that the rules have changed, and he's not happy about it at all. Can he adjust accordingly or will he just be a pile of ash?

Thanks for all the great fics