Marilyn Horowitz (author of “How to Write a Screenplay in 10 Weeks” and creator of The Horowitz System®, award-winning university professor, producer, screenwriter, script consultant and [stops for breath] successful writing coach) has a Twitter stream dedicated to crafting a group screenplay. Follow the tweets, add a line at a time (140 characters only of course) — just send her your next line of the script as a private message at twitter.com/tweetamovie — and watch it grow.