First, do you teach college-age students? Check out Tumblr. You may have heard of it because of its purchase by Yahoo!. It’s a simple blogging/sharing site primarily aimed at images. Text and sound can also be shared, but its focus is on one piece (or highly related set) of content per post.
It’s a little difficult to explain. Like most technology, it’s much easier to understand if you just try using it. You can always delete your account if you don’t like it!
It’s pretty different from the way that people blog at WordPress, for example; the barrier to posting and the expectations of what a post should include are both pretty low. This makes it a lot easier to use. It’s more two-way than most blogs: you can use Tumblr to follow and view other people’s posts, all mixed together, and you can make your own posts/reshare others’. Some people only follow; some post, but rarely; some post prolifically. People in their late teens to mid-20s seem to make up most of the users, and for some of them it’s replaced Facebook as a way to have fun. (Facebook is where your mom checks up on you, after all.) I love art, so I enjoy all the art shared on Tumblr. It also has a major social justice faction, which I appreciate, enjoy, and learn from.
Tumblr could work well for ESL/EFL students: upload a photo and comment on it, reshare an image and say why.
The big caveat is that Tumblr is akin to an unfiltered image search in terms of the chance of seeing a NSFW (not safe for work) image. You can add something called Tumblr Savior that will let you filter things tagged #nsfw, but not everyone uses that tag. Therefore, I would not use Tumblr with students who were not legal adults. If you get used to using it yourself, you can probably think of ways to use it that will minimize problems.