Building upon what's already been said, and it's all true, the best way to find someone to work on a project with you without paying them is to make it a project you do together, rather than them drawing your idea for you. Another way is to find an artist who really enjoys your writing or a particular story and is interested in drawing a good comic. Find some method of showcasing your writing skills in hopes that it will make artists want to make comics with you, and maybe lead to one of the first two. I've done both, to varying levels of success.
I've been lucky enough that my art is passable enough that people forgive its limitations to enjoy the story, and that's drawn the interest of several artists far more talented than I am (actually, that's how I met my wife.) I'm not sure how you could make this work for you if you don't feel your artistic skill is good enough that people will accept it so they can read the story. Maybe a photo comic? Maybe you could post something more prosaic? Find a delivery system for your writing, and try to get that in front of as many eyes as possible.
It helps to be flexible as far as story goes. Just recently, I answered a post in the Collab board, tossed a bunch of ideas at the artist, we talked back and forth about this thing and that thing until we came to an idea that we both liked, and now we're developing that as a comic. Neither of us had preconceived ideas about a specific story, we just started talking and honed-in. Not that I've paid a huge amount of attention to your correspondence with artists, but peripherally it seems you have one idea that you're trying to do. I might be wrong, apologies if I am, but if not, try being more open, or maybe find an artist with an idea that you can both work on together, and use that to let yourself shine.
You could also try working on shorter pieces, stories that don't require as much effort from a single artist. In Pictures of You, I've worked with about 10 guest artists and am going to work with a half-dozen more soon, all drawing little shorts that I write. It's much easier to find someone who'll draw 3-5 pages for you. You could start an anthology comic doing this, and maybe one or more of the artists would be willing to do more with you, and you can develop longer projects based on that.
And just like Pinali and Eishiya say, make friends...or more to the point, get to know artists. When Ben Steeves and I started Our Time in Eden, we knew each other through the local comics scene, but we weren't best friends or anything. I liked his art and he liked my writing, so we talked about the idea of doing some work together. I gave him a couple of scripts I had, one being Eden and the other being Pictures of You. He picked Eden mostly because it was shorter, though between you, me and the internet, it's also the better story.
Don't just rely on the internet, though. If you have a local comic shop, go down to your local comic shop and ask them if they know any artists who might be looking for a project. Even if you don't find an artist, you'll probably meet other comickers that you can talk shop and compare projects with, maybe even get a comics scene going and entice other artists to come hang out.
I guess the bottom line that everyone is saying so far is to build relationships, but don't get bummed if they don't all result in collaborations. The other benefit is that you can find someone you'll enjoy working with, which is more important to the success of a partnership than I could say.