Recently, advertising for a roleplay group in-game seems to be the more "effective" way, since that is where the majority of Feral Heart players are looking. If no one knows that advertising for groups is an option on the forum, most will probably resort to advertising in-game, especially since most people playing the game are playing, well, the game. c:
A few months back, the roleplay boards were a bit more lively in terms of advertisement, but I still see users advertising for roleplay groups on the forum. I think it depends on the type of group, too; for some roleplays, it might make sense to advertise in-game without going through all of the hassle of making a forum advertisement.