You don’t need a critical mass of people to create momentum. You need a critical mass of activity.
Activity is energy that causes members to do amazing, wonderful things. Things like contributing ideas, donating their resources and, sweet joy, inviting their friends.
Highly active communities are self-sustaining and self-recruiting. Making existing members more active now, pays far greater dividends than recruiting new ones tomorrow.
Every day you choose between spending your time growing numbers or increasing activity. I hope you usually choose the latter.