I think one of the biggest reasons that jazz is not as popular is that its not used in movies enough. Why dont you start out by making a resource where u can get samplings / full blown songs for use for free / cheap / subscription. You could probably target the NYU /Colombia crowd studying movie making. Im sure they would love to get their honds on a easy to afford collection of classe/intense background music. You could also offer it as a platform where up and coming bands could offer samples of or full versions of their tracks for free. I dont think that it is possible to help grow a genre based on an app or a site alone however. A multi pronged approach would be necessary. Set up listening sessions where , as jaetldev suggested, you have guided listening starting with the more popesque jazz bands . Get local artisanal breweries to provide the drinks , new restaurants to provide venue and food. you can also feature a local band. People could pay to come get a quick idea of h ow jazz is along with food booze and probably to meet some new interesting people of the opposite sex. This is just off the top of my head after wakinng up from a Huge nightmare so gimme a few and ill try to come up wwith something more interesting.