Yoooohoooo~~!
So this seems to be a thread where I could be of use in.
My name is Reon Merryweather, and I'm... I think I might be allowed to be called an expert at finding artists.
I work with over 15 great artists, and have created loads of webcomics in collaboration with these artists.
Back when I was 16 and had no artists to collaborate with, I tried writing on forums and mass-sending notes on places like DeviantArt and Pixiv. This doesn't work.
You're not going to be very likely to find an artist looking through a webcomic site forum and saying "Hey! This guy needs an artist! Maybe I should draw his story for him!"
And while I agree a good story is just as important as good artwork, artwork takes FAR longer to produce, and it is therefore much more risky for the artist to get involved, than it is for the writer to get involved.
If you are interested in finding a good and high quality artist, I honestly suggest commissioning one to draw a oneshot of your story. You can get a good and high quality artist to draw 50 pages for around 2.500 Dollars.
Of course that's incredibly expensive. Most of us are students, and can't cough up enough money to pay a living wage to an artist working on something that might not even return any profits for a long time.
But what I found is that once you've created a oneshot, that makes other artists you approach more likely to collaborate with you, since they have evidence that you're capable of putting together a story, and have done a succesful collaboration with the artist you commissioned.
Another thing is to always be polite to artists. While an artist might refuse to collaborate with you, being rude to them or even displaying annoyance, can get you on quite a blacklist. A lot of artists that are involved in webcomics are involved with and talk to each other regularly. If someone says "Don't work with that guy, he's a huge asshole" it can hurt you a lot, even if you aren't at fault.
I suggest for you to never ask an artist that is already working on a webcomic. I've met artists who get offended at even the notion that you'd ask them, when they can clearly write stories themselves.
I'm trying not to sound bitter here, because I honestly am not. I couldn't be happier with my position in webcomics today. In addition, people that turn you down might try to suggest some things that might make other artists more likely to accept your job. While this might be done with good intentions, it can turn out quite harmful for you as well. Keep in mind, these are artists that have no intention of working on your story, so take their advice with a bit of salt.
Here here is a thing that you might be adviced to do, which I recommend NOT to.
Never have a script pre-written.
Reason: Artists that are likely to collaborate would most probably prefer to illustrate a story that they have a say in. I suggest letting them pick a genre and set of characters, that they feel comfortable writing, rather than presenting them with a finished story, which can seem alienating, and make them feel like they have no ownership in this story.
If you have any questions, I'd be delighted to respond.