It is much harder to find financial information on private companies than it is for public companies. While public companies are required by law to disclose detailed financial information to the SEC (available from the EDGAR database, Mergent, and Nexis Uni), private companies can decide how much information they wish to make available.
Both Mergent and Nexis Uni have information on private companies.
You can also find news articles about private companies by searching Business Source Complete, Nexis Uni, and Factiva.
Finally, be sure to check the company's website. Each company makes differing amounts of information available publicly, ranging from none to quite a bit. If any information is available, it may be behind small print links with titles like "financial information," "investor information" or "fact sheets."
Company's Website - Almost all companies have websites which divulge varying amounts of information about themselves. In most cases, they will not offer detailed financial information, but sometimes, in an effort to attract investors, they will give some hints. Look for links for Public Relations, Marketing, New Products. Often the links are at the bottom of the page and in small print.
Local Newspapers - Often local newspapers will cover smaller, private, regional businesses that do not make it into the national databases - (see the "Getting Started" tab above for newspaper databases).
The Standard Industrial Classification (SIC) and North American Industry Classification System (NAICS) are numerical classification systems created by the United States government. These systems are used to group/classify like companies into industries for the purposes of collecting, analyzing, and publishing statistical data related to the U.S. business economy. The SIC system was originally developed in the 1930s and was last updated in 1987. The NAICS system was first released in 2002, updated in 2007 and last updated in 2012.
While NAICS has "officially" replaced SIC, many business directories and databases still use one or both of the systems. Therefore, it is important to know about both SIC and NAICS.
Some library databases, books, and web sites allow you to search using SIC and/or NAICS codes. It is very helpful to know what your industry code is before starting your research in Library and government resources.