Ask HN: After I build a prototype, how do I get feedback to 'iterate quickly'?

I have been working on a side project www.schesign.com and have been getting feedback from friends and coworkers, but now I'm ready to get feedback from more people. But my post didn't make it to the front page of HackerNews so it when on and off the new section. Maybe I should be trying to cold email different companies that could be interested? Or maybe make use of Twitter? I've always read about quick iterations and getting feedback quickly, but how do you actually get the feedback for an early stage prototype/product?