Why don't you just go to Union Square and ask people if they'll test your app in exchange for a free coffee. There are TONS of tourists around there, and a lot of them are just sitting around after a long day on their feet.
If you're going to be successful as a startup, you gotta hustle. I did door-to-door sales one summer and do you know which people turned out to be the nicest? The ones with "No solicitation" signs on their door. I kid you not. Just go and do it.