Social media prospecting

Im in the real estate industry. Im focusing the majority of my effort on real life contacts with people through doorknocking. I was cold calling random people but the few people who arent on the DNC list are mostly old people too senile to sign up, they usually tell me they plan to die in the home haha. So Im trying to find ways to generate leads online because running around neighborhoods knocking on doors is tiring. What I really want to find out is a better way to prospect online. Social media looks like a promising medium but Im not too sure how. I have a facebook, linkedin and twitter. Now for facebook I keep in touch with all my friends and let them all know what im up to. When I message people not on my friends list I get a very low response rate, I notice FB says the message goes in the persons "other" folder so perhaps that explains it. I try to keep my messages under 20 per night on FB so I dont get banned for spam or something. Twitter Im not sure how to prospect efficiently with. Linkedin I can add CPAs, tax prep and other referral partners, but how can I reach my target audience of sellers?Once I get a couple things close I want to juice up my marketing(mailers, PPC, etc) so I can relax some.Classified Ads-Working well for buyer leads, Im emailing/calling all the FSBO sellers tooVideo+Blog-Havent implemented yet, want to do 1 of each daily with a focus on communities herePPC to OptIns-Havent implemented yet, but plan toSocial Media-This is what Im trying to figure out, is how to prospect to people on here who I dont know yetGoog Places-Signed up but havent received my postcards yet. Maybe I should have made citations first.