Computer mediated communication (CMC)-- how can i explain text messaging conpared to facebook for an essay?

for an english essay i have to pick to computer mediated communication types, which i have chosen text messaging and facebook. i need to know the pourpose of both the context and audience. i also need to conpare the language used in the two and how it reflects on the audience. please leave the site which you are using to answer so i can refer to it.