Finding users for interviews

Hi there!

I'm a big fan of validating ideas before building them. I really believe that the success (in additional to an exceptional good execution) lies in this phase.

However, one of the biggest challenges for me right now is finding users for interviews.
I don't have a large audience yet. So I was spending a lot of time on finding my defined customer segments on Twitter, cold-messaging them and asking them for an interview. I think I messaged around 60-80 people which resulted in 4 total interviews. This can't be the way to go (if you don't have an audience yet).

The next step was looking into paid solutions like userinterviews.com.
However, either they are WAY too expensive for basic customer interviews, or solutions like craigslist make it also kind of difficult to find people...

Another idea I came up with is putting another test first (e. g. landing page), driving traffic via PPC to it, collecting emails and THEN interviewing the leads.

So here's my question:
How and where do you find people for customer interviews in the early stage (problem interviews, and possibly solution interviews after that)? Do you offer them incentives?