Are your friends/"likers"/followers on Facebook and Twitter engaging in your posts and tweets? Do they like it, do they share it, do they retweet it?
If that is the case, without doing much of it, I am sure that they are already probably helping you because in some way, they know your website and thus share your content.
Now if your answer is no, there goes the problem like several social media account owners, they have big number of likers and followers, but generates only a small number of engagement.
What are some ways of getting your Facebook fans to boost your pagerank?
Your Page on Facebook as well as on Twitter is your platform to promote your website. Thus, post interesting content to keep them interested, and add a link to your website on your posts/images. This will allow them to know that by clicking the link, they could expect more from what you have already offered.
Offer your services/products in ways that are not all "sales talk" by providing them with tips on things.
Your fans can only do the work for you to boost your pagerank if you have been doing a good job at doing the work for them too--giving them new information, exciting concepts, and nice ideas.