Facebook has 700 million members and over half of these visit their Facebook every day.
If you're not on Facebook join now at http://facebook.com.
Once you have joined Facebook you should concentrate on building Facebook Pages - these should be dedicated to your niche or product and this is the main destination for your traffic.
The strength of Facebook is that it is Viral. When somebody becomes your friend by clicking on the Facebook Like button. that fact is automatically transmitted to all of their friends by being posted on their walls. So if someone with 5000 friends "liked" your Page at leasr 5000 would be informed about it and might therefore come to look at and perhaps "like " your Page also!
It is extremely important that your Fanpage be crafted correctly as it should act as a mini website. You should have a welcome page and optin forms at the very least
This is easiest achieved by buying one of the many products out there to help you.
I recommend 2 Facebook tutorials which have both been released since Facebook updated their site. They are the best of what is on the market!
1 Mark Anastasi's FB Auto Cash
http://tiny.cc/FaceBookAutoCash
2. Georgina Lamy's FB ATM
http://tiny.cc/FaceBookATM
Go Daddy
