Well, that's a start.  But you could still write volumes on this topic.  Let's try narrowing our topic further.

Mass Media and its Audience
	an age group	Mass Media & Children Mass Media & Teenagers
	A Location	Mass Media and audiences in the Middle East Mass Media and audiences in Hayward, CA
	an additional topic	How Traditional Mass Media vs. Blogs target their audiences How advertisers sell their products to audiences through the mass media
	a population	Mass Media and Women Mass Media and Asian Americans
	a further subtopic to the "Mass Media"	Newspapers and African Americans The Internet and Older People

It is helpful to write out your topic as a research question. Let's say, after much reflection, you were especially interested in how children are influenced by advertising in the Mass Media's influence on children.  So to phrase it in a question would be like this:

How do advertisers sell products to children through the Mass Media?

Note: While this is manageable, you can further narrow down this topic--for example you may be interested in television advertising to children, or the influence of product placement in cartoons, or how advertising affects children through the Internet.