You already know you can't use sales pitches when talking to Facebook friends. Your friends would find you dull if you did so. But how do you market if you can't use sales messages? By sincerely connecting with your audience.
Members of Facebook are here to communicate and interact with others. We love this connection we have to others throughout the day, learning little bits of what their day is about. Interaction is how you will distinguish yourself in this new arena. Interaction builds trust. Your job is to let people know what you are about without pushing products. But more importantly, you need to get to know what your community members are about too.
The interaction cannot be one-sided. Your friends will see through this very quickly. They want you to engage with them, comment on their updates, view their photos. Show you are taking an interest in them. And here's the most important part; you have to be sincere in your interactions. You have to really take an interest and care about what members are doing and saying. If this is difficult for you, then social networking is not for you.
If you are sincere and do really care about your customers, then get on Facebook and talk to people, comment on their status. Ask them questions. Find out about their families. Your sincerity will show through and you will continue to build strong relationships with your community.