Sometimes Facebook block accounts for sending massive friend requests to unknown persons. After getting blocked, you will not be able to send friend requests on Facebook even to people you personally know. Here is a cool trick that will allow you to send friend requests to people even if you are blocked.
Login to Facebook account and get the email address of the person you want to add to as a friend. Then click here and you will be able to add friends by using different email services. Login with any of those email services and add your required contacts to Facebook.
If you want to add bulk friends then create a notepad file with comma separated email contacts and save it as filename.vcf
Finally upload that file through the previous window and your friend request will be sent to Facebook users with those email addresses.