This software application is described by its authors as:
The first LIWC application was developed as part of an exploratory study of language and disclosure (Francis, 1993; Pennebaker, 1993). As described below, the second version, LIWC2007, is an updated revision of the original application.
Note those dates. Long before social networks were founded, the LIWC was created to analyze large bodies of text — like a book, article, scientific paper, an essay written in an experimental condition, blog entries, or a transcript of a therapy session.
Note the one thing all of these share in common — they are of good length, at minimum 400 words.