Typically, they have to have a registered agent in the county where you are suing (not exactly true, but the clerk might tell you that -- also makes service of the suit much easier).
Go to www.state.nj.us and look for the Secretary of State. It should be under Business and Economy or perhaps State Government or something like that. Look for the company's registered agent. If it's not registered to do business in the state, then that's a whole different can of worms.
Also, you might want to check to see if your state has a guide for consumers/laypeople for proceeding in small claims. It will answer a great many questions for you which will be specific to your state's procedures.
Just did a little digging, and I think you want to start here. Choose the "Status Report Lookup" option toward the bottom. You can look up the company there.