A 2016 return can no longer be efiled. It has to be printed, signed, and mailed. Did you start one online earlier and now need to finish? If so, that would require 2016 desktop software. We can tell you how to finish if that's your situation.
I would recommend mailing with a method that has tracking, such as Priority Mail or certified return receipt.
Approximately 4 weeks after mailing, it should start showing up in this IRS status tool:
http://www.irs.gov/Refunds