Good advice. I am currently working with four separate artists on various Star Wars related web comic projects. I find that getting an artist to collaborate with is really about having a geniune infectious excitement for the project you are creating. If you aren't excited about it, you artist isn't going to get excited about it, and that is the key. The second you get that artist excited about your story idea, that's when you have them. This is really important since a writer's workload on a webcomic is so much less than the artist's.
Another thing that I find breeds success in an artist hunt is to be personal. A random post asking for ANY artist will get you NO artists. Go to deviant art, or look at portfolio pages. Email artists specifically commenting on what you like about their work specifically, and why you think THEY would be the perfect artist to collaborate with. If your artist feels like they just got picked out of thousands of other artists, its gonna make them a lot more interested in what you have to say. It is kind of like going to a club and trying to pick up a girl. If you walk in and just scream hey, will any girl dance with me, you aren't going to get any ladies. You have to go up to each one personally and ask them specifically. Then it becomes a numbers game.
Another side of things is how to keep your artist happy once you get one. I usually talk to my guys (and girl) 4-5 times a week online, sometimes not about the comic at all. By creating that mutual friendship, and not just having a strictly business relationship, your artist might be more into the comic. Also, if all you talk about is the comic, your artist can begin to feel like you are hounding him for pages. A little small talk goes a long way.
The quickest way to lose an artist is to stifle their creative freedom. You can't be a nazi dictator of the story. You have to be open to changes in the script and page layouts. If the artist wants to do something differently, and you strongly disagree, don't just lay the hammer down. Explain why you need it the way it is. A good artist should be focused on serving the story anyway, so if there is a plot reason, they ought to agree. Otherwise, I would suggest trying to rearrange some things. It is just very important to stay flexible.
Talk with your artist before you get too far into writing. One of the first things I like to do when starting a new project is to ask my artist if there is anything specific they want to draw. Even on projects that are already written but trying to find an artist for, when I do find an artist, I still have that conversation, and see if there are places to fit things in for them. A certain character, environment, creature, etc. Find out what they want to be drawing. Then keep that in your head when you are developing your plot and script, and see if you can't work at least a few of those things in. This not only gives your artist something to look forward to when drawing, but it makes them really feel like they are a part of the development process.
Finally, and this might seem contradictory, but push your artist. Try and get them in the mindset of taking their work to a higher level. Let them know you are interested in helping them hone their craft, and that when the project ends, they will be a better artist for it. Write scenes that are going to push them. If their experience tends to be a lot of pin ups or action splash pages, challenge them with a few emotional scenes that require a mastery of expressions. Don't overdo it, or you will push the artist away by overwhelming them. But you have to challenge them enough to keep them interested. If they are a traditional comic artist, try having them paint a cover for the book. Giving an artist new challenges is really important to their satisfaction.
Anyway, just a few more tips for you fellow writers out there. Artists, would be curious to see your responses to these tips. Anyway, happy webcomicing!