Comment by blitzar
Bring back some old school methods with a modern twist too - upload all your contacts.
Instead of just emailing everyone inviting them to join and telling them which kind friend reccomended they join - use the birthday and home address information and send them real tangible marketing material for their birthday (+ on Anniversaries, Christmas, Easter and on any day ending with a "y").
That's may need over million TB to collect all data, actually is there anyway to host they data without doing cloud or Hardiver things in the world?