Hard to say with no information, but...

I would always suggest starting with the community your customers belong to.

1. Try and get relevant music blogs writing about your app.
2. Look for tweeters who are big influencers of your potential customers and see if you can get them interested in tweeting
3. Try creating some incentive for people to share the app with their friends / peers
4. Write your own content for your website or a blog, good quality content is what google looks for these days
5. Decide based on your markets demographics what other networks are good to establish a following on and create useful content there, e.g. instagram