Show Your Usefulness
If you want people to join your MonkeyJar troop, you´re going to have to spell out for them, what exactly they are getting. Explain the money they´ll be saving, the time and gas they´ll save when shopping online. Make sure they´re aware of how MonkeyJar works. You´ll really have to sell the concept but once you do, they should be all about it.
Showing someone, quantitatively, how you can help them is always the best way to go when you are truly helping them. Which is exactly what you are doing by introducing them to your MonkeyJar troop.