Firstly, they encouraged people to add their friends and family so that they can share content within their circle on Facebook.
Secondly, Facebook sent emails to their friends and family inviting them to create an account with Facebook.
This growth hack piqued the interest of many as they became curious about who tagged or mentioned them on Facebook. They wanted to see what was being told about them on Facebook. Also, they wanted to see what would they get after signing up.