They could also be on holiday abroad at the minute. Check out their username profile (or ask one of the mods to have a look) and find out when they last posted on here. I'm sure admin/ Pet/ Stu can access the last time they even visited the site (and not necessarily posted anything).

If they've been on during this time, then they're takin the pee & they need naming. It may be the only way to get them to respond.