How do you find a starving crowd ?

What the whole starving crowd thingy is about is
to find the starving crowd before you pick or
develop the product/service for them. Don't know
what your product or service is, but who wants it?
who needs it? where on the internet would that
kind of person hang out?

> I've read that if you want to market a
> product, the first thing you need to find is
> a "starving crowd". That is, find
> a crowd which is hungry for what you have to
> sell.

> My question is how do you find a starving
> crowd on the internet? Is their a good
> technique to do this?