1. You aren't finding anything, or only one or two things that don't really seem quite right.
2. You've found a few GREAT articles or books, but you need 6 or 50 more.
Check the Works Cited or Bibliography or References lists from the great sources that you've already located.
Try this first:
Other databases of interest:
A quick word about search engines (i.e. Google) vs. library databases
The search box looks the same, but the underlying structure is different. Google and it's brethren are easy-going, they'll take what you give them and return something fairly relevant. Library databases (the library catalog, Sociological Abstracts, etc.) are picky. They want you to be brief and choose your search terms carefully.
General advice