There's a new critic in television writing rooms pressuring some producers to tweak scripts: the Twitterati.

Comments posted on Twitter and other social-media websites about television shows have exploded in the past year, to 75.5 million in July from 8.8 million a year earlier, far faster than overall growth in such comments, according to research firm Bluefin Labs. And the comments are beginning to have an impact on the writing of shows.

Writers...