I'm sure you're all familiar with the chain story as a form of writing exercise, but today I'll present a little spin to the activity. You can use this method whenever you want, but let's take an example of dealing with conditional sentences. When practicing conditionals, you should start a sentence with: "If I was a rock star..." and a student should continue the sentence with their own words, e.g. "If I was a rock star, I would be very popular." Then another student should continue like this: "If I was very popular ...". You do this until everyone has said their own sentence.
You can also use some alternatives and here is where Twitter comes in. As you all know, a Twitter message can contain up to 140 signs, so you can tell your students to write their example as long as possible, but no longer than 140 signs. They can do this on paper or really use their Twitter accounts if they have them. Twitter is even better for real chain stories, where students have to write their sentences based on only the last sentence before theirs. Those are really funny to read at the end.
They could do this on their Facebook accounts as well, or if you have a Facebook group for a certain class, you could start a story in a post and then they could write the rest of it in the comments. This would be a great homework, since they probably spend a lot of time on Facebook and it wouldn't feel like a real homework.
Do you use social networks in your classroom? How?