Private Companies don't have the same filing requirements as public companies, but you may still be able to find some (typically more limited) information.
Business and financial data on major, non-publicly traded corporations, including family-owned, private equity owned, venture backed and international unlisted companies.
Covers all areas of business. Industry reports and company profiles include some international companies. For company profiles, try the Company Profiles search (look for the Company Information link in the blue navigation bar near the top of the screen.
Companies are required to file with the Secretary of State (or a similar entity) of the state in which they are established. Please note that information about private companies will be extremely limited and may not be available online.