1) Do you have a website?
2) Emailing list?
3) Any social media presence?
4) Presence is any online communities where the target market for your app hang out?
5) Do you have any budget for PPC? Even a small daily budget might at least get a trial customer or two.
Ultimately, you just want people using it and giving feedback. I say that because it's a different marketing mindset than looking for growth.