strategy
The 11 Best Growth Hacking Strategies to Skyrocket Your User Base
https://optinmonster.com/growth-hacking-strategies/
friends invitation
Invite Email Contacts & 4 Other Hidden Facebook Features You NEED to Know
https://www.wordstream.com/blog/ws/2015/10/26/facebook-featuresDribbble - full-view.png by Julia Khusainova
https://dribbble.com/shots/1113132-Invite-friends/attachments/140946Friends Inviter plugin for SocialEngine - Hire-Experts
https://www.hire-experts.com/social-engine/friends-inviter-facebook-plugin