Zone chat is beyond useless for this, thanks to the rather high prevalence of trolls deliberately misleading people. You'll probably have to join a guild dedicated to this part of the game if you want anything resembling reliable information in game.

Also, they don't show up right away when the sun goes down. Plan on spending most of the in game night in the zone. There will be a lot of people in zone chat saying they don't spawn that night. There's a very good probability that they are either misinformed or trying to trick you. Until that sun rises, don't believe them.

And pay attention to the moons. General consensus is that if it's not full moons, there won't be werewolves. New moons for vampires. And no, it doesn't have to be completely full or new. They show up around that phase, which I think might be throwing some people off concerning their importance.

One more thing. The spot by Dune is pretty worthless as well. Lots of trolls like to hang out there and spam AoE and/or try to kill the things before anyone gets bit. Try and find one that doesn't have people spamming stuff. Wander around and explore.