Once you have established a topic and an area of study, it is important to find research similar to your chosen area. Remember, no one will have done exactly the research you will be doing. You might find others that have done research using a different medium or a different group of subjects. Other will have studied portions of your topic. These are the articles and studies that will go into your literature review.
Make use of subjects, synonyms, and bibliographies to find those studies. Others may have used the same communication theory to ground their research.
All of these are potential sources for your literature review.