A company website is the first place that everyone should visit to get information. Visit "About Us", "Products and Services", "Mission Statement" etc. pages on the website. You should also go on "News & Updates" to know recent events happened and any other news on the company. Some websites also have Blog and employee related pages also , if yes, visit them also.
3. Companies review websitesAnother good tool is social media, Facebook, Twitter, Google+ and Linkedin, etc. Nowadays every company is available on social media, especially on Linkedin as it is a platform for professionals. So you can search on linked and read about the company.
5. Connect to employeesDo a search on Google, Bing or YouTube about the company. Use different keywords to find positive and negative information. You can find information about customers, positive or negative feedback, legal activities against the company (if any) etc.
Linkedin is the best place to find out the current and ex employees of any company. You can connect to them through email, phone or leave a message on Linkedin itself. Ask questions about company, working environment and management etc.