To Gain and to Give: Hilchot Tzedakah, Day 8
It is a great mitzvah to serve as a gabbai tzedakah, i.e. one who encourages others to give tzedakah. This includes anyone who is actively involved in soliciting or enlisting others to give tzedakah, i.e. one who encourages friends or family to contribute to a cause or one who makes phone solicitations on behalf of a dinner. Chazal tell us that the reward of one who encourages others to give is greater than that of the giver.
שו"ע ס' רמט ס"ה