The AOL exodus continues. America Online SVP of Global Messaging David Liu is stepping down next month. Liu worked at AOL for only a year and a half. Liu was the man behind hiring Brad Garlinghouse from Yahoo! Garlinghouse is now going to be responsible for AIM/ICQ, AOL SMS services, and AOL E-mail (“You’ve got mail”). Liu also helped integrate Twitter, Facebook, and other social networks with AOL services. No word yet on where Liu is headed, but this post will be updated when we find out.