One good place to start for determining if a firm is publicly or privately held is Mergent Intellect, which provides the well-known “Hoover’s/Dun & Bradstreet” company profiles. Another good quick option is LexisNexis Company Dossier, and a third would be ReferenceUSA. What you'll be looking for is a designation of the firm as "Public" or "Private." If the company is public, you will also see a stock ticker symbol.
It may also occur that your particular company is a subsidiary or division of a publicly-held company, such that you will not find financials, etc., on this division, Instead you'll have to go to the parent, publicly-held firm for main financials, and see what possible information may be stated about segments or division performance.