I sell music on AudioJungle. I use a combination of Youtube and Soundcloud to brings buyers to the site here. For every song I have in my portfolio I make a video on Youtube for it with a link back to the site here (yay referrals!) and same for Soundcloud. I also created a private group on Soundcloud where i submit all of my tracks and no one else can and I believe many buyers come from there as well.
My main platform is SoundCloud. With almost 1000 followers and Pro Unlimited membership I have average 200-300 (sometimes more) listens per day and pretty nice referal traffic.
Second is Facebook, which is also nice. You can share some your thoughts, photos, new music pieces and so on. Lots of customers come to my facebook page to ask for some audio tweaks, or even custom job. But I had negative experience with it, when I started promoting it for some $. Well, one of the worst money investing. I guess it might works when you put lots of bucks in it.
I also have Youtube,Twitter,Pinterest, Linkedin etc,but I can not evlove them all yet. I think this might be my future goal.