I THINK YOU JUST PROMOTED IT! HA!
All jokes aside, I think you just took the best first step. You promoted on a site you are both comfortable with and reaches your target audience. Now take that to linkedin, and Facebook, and instagram, and foursquare, and google plus (def do this one as it shows up in google searches), and twitter, and pintrest. Once you’ve hit those then you continue to follow up with forums etc. Pound the social media pavement (But don’t overwhelm us with stuff, keep it real and from the heart). I know this is general, but it really is the best way to passively hit trainers, we’re on those sites.
If you want some more ideas from your target audience (me) feel free to contact me. We’re always looking for new ways to help our communities. I’m done a lot of app beta testing for fitness companies so I know what I like and what I don’t and where some of failed and some have succeeded.
Hope this helps,