I wouldn't sweat it. I worked for multiple staffing agencies over the summer while in school, and most if not all either got bought out by another company, went out of business, or the parent company only appears on my SS print out. For the most part all of the companies that went out of business have a c/o attorney name and address under the company name. Use the information from your the Social Security print out and you will be good. The company you worked for might have been a subsidiary in any event its the parent company that was cutting you a check.
Good Luck!!!!!!!!!!!!