How to get referrals by advertising?

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I have been getting referrals freely by some normal referral making methods like posting in forums,chatting , mailing,blogging etc.But i get very few referrals from these methods and most of them are inactive..So now i want to know how to get referrals by advertising.I want referrals mainly for ptc(neobux,clixsense,infinitybux ) and gpt(prizelive) sites.I can invest only upto 5$.Which sites are best to advertise and get referrals ?