I used Edmodo in class this past year. I did not have much success, but I did start it during the 2nd 9 weeks. For the upcoming year, I plan on starting this during the first week and setting expectations.
I chose to use Wallwisher. This would be a great place to post notes from class, vocabulary words, or examples. It was easy to create.
I could allow the students to review the wall during warm up time.