I guess this might work for casual contacts, but less effectively for building an everyday relationship, except for the vast spectrum of the forum participants, which seems to be across north America.
from the Posters comments. it seems most poly relationships start when one member of an existing relationship introduces contact with another.
For a man, the biggest hurdle for someone not in a relationship, is to initiate a concienscious, honest contact without seeming like a just a creep trolling for gratuitious 3 way sex.
If a woman wanted to initiate the approach, any standard media such as a "wfwm" or "wfbiw" on an anonymous site like Craigs List or something, would bring out the creeps or at least only women seeking another women for one on one relationship.