Hello.
Is there a way to OOC leave a message for another character's player, without knowing who they are on the forums or revealing who you are, in order to schedule a likely time to meet up and play?
Short answer: No
Long answer: You'd have to go through the staff, via the request tool, and mention your need in a character report. If it's clan-related, CC the concerned clan on the report. They're probably not going to help coordinate trivial things like a Kruth game or booty call, but if you're trying to get in contact with a clan leader for hiring or some other official clan business they might be willing to help out. [NOTE: However, consider that if you're not seeing a lot of leaders/members of a specific clan online during your usual play hours, you're going to have a very hard time meeting up with them frequently even if you do manage to get hired by that clan.]
Thank you for the reply and the advice. It's really helpful.
There are some clans where there is enough movement among the minions, like some military clans and the Byn where even if you don't see the hiring people there's a value to joining anyway. Especially if you're meeting those minions and would like to be one. In those instances, definitely send a request with regards to your trouble getting hired. With the exception of the Byn and the military clans when they're active, Moe is right. You don't want to join a clan where you don't get to interact with the leaders.