It depends upon your server, actually. On Kane Bayle all LDoN recruiting takes place in the Plane of Knowledge, as far as I can tell. At least, since the most common adventure by far is the Butcherblock one, and whenever I am in that zone I never see any lfg spam, I have to assume that groups only very rarely form there. Occasionally I will see someone who is lfg sitting in the Adventurer's Camp, I assume either because they don't have the PoP expansion or they would just rather be there instead of PoK. But I only see them when I have a full group (or they are outside our level range) so I've never picked anyone up that way.
Since it's so server dependant I see no reason why you shouldn't just do an ooc on your server to ask people where the typical place groups form is.
Game on,