Go to www.facebook.com/hacked and select the "my account is compromised" option. After that, carefully identify the account by entering the username, email address, or mobile number. Now, Facebook will prompt you with a series of security questions, including the account's old password, if you enter the captcha (special code) in the "security check" option. The complaint will be sent to Facebook if you correctly respond to the questions and select the submit button.