Like members, moderators have the option of logging out of the instant message system and can choose not to appear in the directory or "Active Now" lists, so you cannot tell which moderators or admins are on the site at any given time. Moreover, our moderators are unpaid volunteers who help catch things during their normal use of the site, so we ask that you not contact them directly with issues. They're not on any kind of schedule or rotation.
However, if you have an issue, you can report content, use the feedback button, use the contact admin button, or send Just Asking an email. You'll receive a response as quickly as possible.