A way to increase contributions (perhaps dramatically) especially from the younger, would be to offer tangible rewards for completed tasks. Reward(s) could be given in exchange for accumulated contribution points much in the way businesses give customers loyalty or reward points for the continued purchase of their product.
This has been proven effective.
The rewards to be offered for this, whether physical merchandise, "E-gifts" that can be redeemed online or even currency could be donated by organizations and corporations.

Forgive me if this has already been suggested.