The social sciences, like all other sciences, are cumulative in their knowledge. Therefore, it is far more efficient to search backwards from later sources to earlier ones. When you find articles or books that are directly related to your topic, look at their notes and bibliographies for guidance to earlier research.
Reference librarians are always excellent sources for advice on any search.
The first place to start a literature search is in the University Library. Communication Abstracts is issued six times a year and covers journals in communication, related social sciences, law, history, cultural studies, etc. Each volume contains a subject index in the back with references to major theories and areas of research. Each page contains detailed abstracts of two recent articles in the field. The University Library's Research Gateway gives you access to many other important online bibliographic sources, including electronic journals and bibliographic sources.