You can buy FB ads that target the friends of those that liked your page. It narrows the target, but as each one joins, your target widens. FB puts an estimate on the amount of people the ad targets, I found my estimates were low, not allowing me to run the ad, but I was trying it on a page with only 15 likes. Those 15 like has an estimated reach of only 20 people when using the target friends feature. Write up an ad saying something along the lines of their friend liked the page, so should they. FB does do some social targeting where they put the "Chrarles likes BHW", this may make them show those more often since one of their friends did like your page. They have done it on one of my ads only 1.6% today, but I am sure it helps. I bet the conversions are higher, which is FB's goal, but it likely takes up more space. When I get the chance, I will actually test this out, but right now my page is not big enough. If anyone has done it, or tries it and see a big difference, please post it here.