at the top left of your screen there is a box with a padlock on it, next to a note that probably says "no new message(s)". Click on that. There will be a box labelled "Send a Private Message to". Type "AnandTech Moderator" in that box, then click "Send Message".
It doesn't matter whether a mod is online at the time. The PM will be saved. It may be a while before you get an answer, as the mod who locked your thread might not be around at the time. Also, some mods are simply nicer than others at answering PMs and explaining reasons for locked threads. You may never get an answer.