Crocuta has mentioned one already which is #webcomicchat and I think that's the best one. Another is #webcomichour which is also good but goes a bit deeper into things than I can go sometimes.
It's best to see it as a chance to chat about comics and network because people aren't really promoting themselves that heavily but I always get at least a couple of followers every week and enjoy the chat too. I found and added you on Twitter btw so you can use my Twitter feed for guidance. I've done two webcomicchat's now.
And basically you go on at the right time (it's about 2:30pm West coat America time I think so evening in Europe) and as they ask questions, you reply and check the hashtag in search for what other people have said. It lasts about half an hour or slightly more.