NAU doesn't have a policy against using Facebook for classes, but it's a good idea to examine your teaching and learning goals before you decide to use Facebook, Google+, Twitter, or other social networking sites. Other tools might be better suited for your purposes. Contact one of our instructional designers for assistance in deciding how to select an appropriate tool.
Two potential problems with using Facebook are FERPA restrictions and Facebook's terms of service. Be sure you understand the implications of both before you set up a Facebook group or page for your class. Because Facebook groups can be private, they are often a better choice for classes.
You must also follow NAU's business rules about records retention—that is, how long student work must be kept available in the event of incompletes and grade appeals (.doc). Any class work you conduct through Facebook is subject to those same requirements, but you personally are responsible for maintaining backups of your Facebook content for the required length of time, because Facebook isn't a university-supported tool.
For more information about Facebook in general, see Facebook Basics.