[pibetaphi2013]

re: other greeks philanthropy events.

Several groups on my campus operate on a point system, and that seems to be really effective. Depending on your bylaws, etc. you could assign a point value for attending and or participating in each type of event. Assign a monthly or semesterly minimum and have either a reward for achievement or a punishment for members who don't meet the minimum (social probation, cannot attend formal, etc.)
Point systems are nice because members still have some choice in which events they attend, and it prevents making everything mandatory, but still encourages participation.