Adding in - as a Branding Exercise Facebook works well. It could also work for entrance level requirements, for a strong brand people are anyway interested in working with ( say Marriott, or IBM for example )....
BUT there are several companies who - for various reasons ( particularly sensitive, senior level requirements ) would not advertise anywhere, including FB. Likewise, many candidates are "passive" till approached for a position which could make them "active ".
As some Recruiters involved in Senior level assignments may have experienced, there are situations where even the possible candidates are suggested by the Company themselves, yet not approached direct. We had such a situation couple of years ago. In the process the Client saved about rs. 5 lacs in the per annum salary bill - quite more than what they paid us :-)
So, it really depends upon what the situation is... you could find us on FB at :
https://www.facebook.com/MyTopJob