If your wholesaling REO's, I assuming your speaking of buyer leads.
I agree with the previous post about craigslist and backpage. Using those see to market to buyers works well for me. The best way do this is not by simply posting deals but to have a teaser description of the deal and a link to a squeeze page that will get them to give you their email address, name etc....and then to send the deals to their inbox.
Its a little game of "give something, get something" by it WORKS!!!