Article searching can be a good way to find information on products or services to help you determine whether or not such a venture serves a need in the marketplace. Other people may have already written about the type of product or service you are investigating, and the information you find can help you determine if your product or service would be successful.
Public companies are required to file quarterly earning reports and other information with the Securities and Exchange Commission, and investment banks publish analyst reports on them on a regular basis.
Unlike public companies, private companies are not regulated by the federal government. Therefore, it is at the discretion of a private company if, and what, they want to disclose about themselves. It can be more difficult and time consuming to locate information about private companies.
UW-Madison has several useful tutorials on how to use Simmons Insights (predecessor to MRI-Simmons Catalyst):