Whether you want to meet agents, editors, other writers, or even connect with your target audience, Twitter can do it all. I'm amazed at how many writers I know who still don't Twitter. I don't know of any other site out there where agents and editors will follow an unpublished writer. If you're looking for the new place to be discovered, I've found it. Just look at my followers. My book isn't published yet and I already have agents, editors, published authors, and producers following me. I'm close mind you, but not there yet.
While I didn't meet my agent on Twitter I did use Twitter to help me decide who I should submit to. And yes, he was on there. Reading his tweets was a huge help in deciding if he was right for me. I saw how hard he worked and how much he advertised his clients. Those are priceless tidbits of information when you're figuring out who to submit to.
Before you jump in be sure to read Jane Friedman's (from Writer's Digest) article on Twitter Tips for writers:
So how do you get started meeting the right people? Reach out. There are several great chats on Twitter for writers, sometimes more than one in a day. Rather than rehash all of them (and there are a LOT) I'll give you this link to Inkygirl.com who wrote a fantastic entry on the subject: http://www.inkygirl.com/twitter-chats-for-writers/ You never know who you'll meet or who will end up following you because they found you on a chat. Hope to see you there!