I have some questions for a friend who is starting a SR4 game. One of his characters has a background in breaking up a small slaving and human trafficking ring in Seattle - mostly out of UCAS prostitutes from Russia / Asia, that kind of thing - and I am wondering if there is any background fluff for this kind of activity in the game?

Tanamous runs organs, so who runs the still-warm flesh?

The game looks like it is starting out in the Barrens, so please address the subject in a manner that is contextual to the Barrens if at all possible. A general overview will do, though.

The same as in the real world, the Russian and Asia crime families.

There would also be some human trafficking coming out of the NAN (mostly SINless Anglos that butt heads with the law).

Until Vice comes out and talks all about Human Trafficking and various criminal enterprises, I'd recommend looking up Loose Alliances and the Underworld Sourcebook. New Seattle and Runner Havens also take a look at the criminal presence in Seattle and what they do.

One of the Seattle syndicates, (I think it's an Amerind syndicate) has a particularly nasty habit of selling people to megacorps who want to test new medications and guns...

Before Ghost Cartels came out, I was pretty sure that the Kumon'go Seloupa Ring did some human trafficking.

Runner Havens does mention that the Black Chrysanthemums Triad in Hong Kong trafficks people to Seattle and San Francisco. They are a particularly nasty Triad, described in length in both Runner Havens and Ghost Cartels. They aren't the only ones who do this sort of thing, even in Hong Kong, but they are particularly known for it (and the related organlegging business from "cargo" that doesn't survive the trip).

All "organized" criminals are willing to do this. Motorcycle gangs these days often run strings of prostitutes, controlling them with very believable threats of violence. As do street gangs.

For a recent Seattle example see here.

The reason why teenage runaways tend to end poorly is that there is no shortage of people looking to misuse them.

I did a bit of digging on the various SR wiki out there and could find very little in the way of direct mention on this topic.

Can anyone be more specific about the factions / people / extent of organization? I have no problem making this kind of thing up, but knowing what the canon universe has to say on the subject can help keep things in a continuity.

I figured that it was going to be mostly Triads and Vory - Triads in the form of workers and some girls and Vory mostly in the form of prostitution rings; much as things are now. I imagine that the Mafia takes a dim view of these things and the Yakuza, outside of indentured servitude of a kind, do as well.

I also imagine that there are probably some thriving human trafficking markets along the highways in the old Western United States.

Runner Havens makes several references to human trafficking being conducted by both the Vory and The Triad. Wasted residents of the Barrens are easy to make disappear and with Seattle being a huge port city, metahumans can be brought in and out of the city with ease. I haven't come across anything TOO detailed covering the subject and suspect that short of a printed adventure or two, you may have to make up any particular players in the business. Check out Season 2 of the Wire if you want a little more inspiration.

As BishopMcQ mentioned above, expect some more discussion of this topic in the upcoming Vice sourcebook. If you want to know more about the factions, people, extent of organizations, etc., I very much suggest picking up Runner Havens. It not only covers the Seattle syndicates that would do this sort of thing, but since it also includes a large chapter on Hong Kong, it can give you ideas of who is operating on the opposite end of the trafficking operation (not only are the Hong Kong triads detailed there, but also the Hong Kong Vory). Then you can pick which outfits you want to use.

EDIT: And I just finished watching Season 2 of The Wire a few days ago and I totally agree with LamplightSlasher's suggestion.