Ask HN: Getting very early customer feedback

I'm trying to get some early feedback before I spend much time building out my product. I like my idea, but, in the interest of customer development, I want to make sure I'm building the right things. So I put together a survey. I've advertised it on forums, LinkedIn groups, Twitter, Facebook, and other places that target the people I'm interested in (which happen to be "entrepreneurs"). I've gotten 11 responses. How can I get more responses to guide my product development?