I've recruited for my online games on various message boards. Most have a recruiting section, even ones designated for online games. I met with success on the Wizards forum that way and ended up with a good player.
I also asked my existing online players, who I met through various online games I joined and writing forums, if they knew anyone. That usually nets a few more players, though if you don't know them and their personalities, you run the risk of including someone you later have to kick or who leaves on their own. But that is inevitable in just about every long game, whether from varying play styles, conflicting schedules, or incompatibility. Don't get discouraged! And if you're more of a mind to run shorter games, something like the upcoming Tomb of Horrors, you might even have more success because of the hype of the new product and the fact it's less commitment in the long term.
Also, online games can be a very flaky thing if you don't have serious players. I use a blog and a forum to help anchor and inform them, and I chat with them via instant message often. They've actually branched off and begun writing their own character journals, short fiction and even posted rp they've done out of game amongst themselves.
I completed my first successful 3 year online campaign in 2008. And I've now been running another game which has lasted 75 weeks which may prove to be a 3 year commitment in the end (we're only level 13 heading all the way to 30). We use mIRC and Maptool instead of chat clients, but that's because my I and my players tend to favor creative writing. Also with various rooms open at once, you can really facilitate characters branching off, offer dream sequences or secret information gleaned from passive or active checks, and a bunch of other private sort of things (which maybe you can do with voice programs).
