Despite dressing in black, wielding a red (if pretty ragged looking) lightsaber, and demonstrating force-like powers in the trailers, it seems there's a very simple reason why Mr. Ren doesn't go by "Darth". "Kylo Ren is not a Sith," reveals Abrams. "He works under Supreme Leader Snoke, who is a powerful figure on the Dark Side of the Force.” Snoke is the motion capture character that'll be played by Andy Serkis, and from the sounds of things he at least may turn out to be a Sith Lord. There's a rumor doing the rounds that he's actually Darth Plagueis, but that remains to be seen.
Abrams also gives some new info on the army these two will be using to do their bidding: The First Order. It turns out they're not the remnants of the Empire at all, and more a fanatical group that's trying to continue their work and may even worship Darth Vader as some sort of dark saint.
“That all came out of conversations about what would have happened if the Nazis all went to Argentina but then started working together again? What could be born of that? Could The First Order exist as a group that actually admired The Empire? Could the work of The Empire be seen as unfulfilled? And could Vader be a martyr? Could there be a need to see through what didn’t get done?”