The official Empire Facebook page can be found here:
In addition to the nation-specific forum boards below, there are a number of (unofficial) Facebook groups for the various nations. These are:
There are also unofficial Facebook groups for the various lineages:
There are also various groups for crew communication, including a general Crew group and specific groups for some teams. Your team leader should be able to point you at them if you are a crew member.
The most common tags people use to talk about Empire are
Remember on Tumblr only the first three of your tags get globally indexed, the rest only apply to your blog.
The hashtag people use for talking about Empire on Twitter is #EmpireLRP
EmpireFiction is an unofficial Livejournal community for personal, background, and speculative fiction about Empire.