with ~pbads, don't be afraid of posting multiple times throughout the period of a day or two. like, obviously wait until your old ad is off the front page, haha, but. you can also cross-post to all the generic ad comms-- easel, rpads, wanna_rp, pb_pimp, etc--if you feel bad about spamming just wait a few hours or days in between posts.
depending on then nature of your comm, it may also fit darkersls, which gets a decent amount of traffic, or anythingbuthp.