Or perhaps all of your friends are married, or liberal arts majors who have absolutely no interest in starting a startup?
Not all of us run in the right circles.
This can be a problem, but there's an excellent solution. You should start attending user groups, be they Python, or Lisp, or whatever. If you can't find a local user group, start one. Give presentations, ask questions, get strangers excited about your idea.
That's true, but why not go and run in those 'right' circles then?
Yes, it's possible that you'd be a great co-founder, and that you have a great idea -- but if you're looking and can't find anyone willing to sign onto your idea, stop for a moment to ask yourself if it's remotely possible that either (a) you're not very attractive as a co-founder, or (b) your fantastic idea isn't actually quite so fantastic as you thought.
Being enthusiastic is good, but sometimes realism is also good.