Soundcloud and facebook seems to be the best place to do it online at the moment, getting a paid soundcloud account and posting to lots of groups is a good technique. If you hop on google you’ll find loads of companies that will work on your promotion for a fee.
But as someone who has spent vast swathes of time promoting music that people aren’t massively interested in, I’ve learned the key to getting your band known is to work really really hard at making your music awesome, making it stand out. If it’s a cut above, people will share it and promote it for you
Great art doesn’t stay a secret for long