You can advertising on FB to drive people to your website to signup on your lead page as one option. You can also drive them to your website and then popup a box asking for their name and email address. You can also use what are called Facebook Lead Ads, which allow you to advertising on Facebook and just popup a lead form or contact form right on Facebook without them having to leave Facebook and go to your site. In this instance, the form is pre-populated with their Facebook contact information which is nice, and these ads can be targeted to either a targeted audience on Facebook based on interests, to your Facebook page like (fans), and/or to your email database that you had previously, which you can upload into Facebook to create what's called a Custom Audience. Each more or less has it's advantage. For instance, when you drive them to your website you can give them more information before they give you their contact info. In the instance of Facebook Lead Ads you attempt to get their info right away so it quicker.