You need to open their eyes--don't expect folks who signed up for your beta to just see what it is to make the leap of, "Oh, I can use it for this!" TELL THEM WHAT TO USE IT FOR. Show them how to use it. Do you have a Getting Started guide? I couldn't find one. You tell me it integrates with Jira, GitHub, and Basecamp. Super. Integrates how? Show me!
Tell me who I am. Tell me who I'm soliciting feedback from. Tell me why it's better right on the site. Don't expect people to just "figure it out." None of your beta users are familiar with your app. You are the only expert.
I did sign up and was left puzzled by what to do next - I wanted to try the functionality but the only example I could see was to send feedback to you, and I couldn't see the tools mentioned on the home page.
I suspect nobody can work out how to get started with your product!
a) Why didn't you ask that explicitly - you need to think really hard about
a1) the questions you ask,
a2) why you ask them,
a3) what answers you expect,
a4) why you got something other than expected, and
a5) what you will do with the answers.
If your question/answer pairs aren't actionable, then your questions are wrong and you need to ask something different.
b) You need to engage your existing users directly. Don't spam them, but send an email along the lines of:
b1) Hiya - you signed up for XXXX and I was wondering how I could help you today? Or better,
b2) I noticed you haven't used YYYY, which I think is one of the most useful features - can I talk you through using it and save you time and money?