Probably there is mistake in FB campaign.
Reward:
100-300 friends - 2 shares/week.
300-700 friends - 4 shares/week.
700-1200 friends - 8 shares/week.
More than 1200 friends - 10 shares/week.
You must have more than 700 real friends.
It will be minimum 700 after the 3rd week for new participants.