Go to the sign in page of the product (for Google Accounts it is myaccount.google.com). Enter your Gmail username (everything that appears before '@gmail.com'). Enter your password.

Check your credit reports. Pulling your credit report and credit score is the most accurate and convenient way to find all of the accounts that have been reported in your name. Your credit report will display every open account in your name, from bank accounts to credit cards and more.

Go to http://accounts.google.com/signin/usernamerecovery and enter any email accounts or phone numbers that you've had for a while and which may have been used as recovery info. The “find your email” page can help you locate any forgotten Google accounts.