Write it down!
Write down everyone you know. This will be a living document. Each time you have an event you'll return to this document and be reminded who might be interested in your event.
If possible, categorize/group your list. That way you'll be able to look at it and say, "Ok, I want to invite student-athletes to this event." and you'll be able to quickly sort out your student athletes.
Don't just stop at the people you know, but consider the people that those people know too!
See the people others don't see
Start seeing the people around you. Not just the people you always interact with, like your family and friends, but all the people around you. As you become aware of others, you'll start to notice things about them: if they're having a good day or not, how pleasant/helpful they can be, and other needs they might have (family, health, financial, etc). The more you tune into the lives of others, the more you become aware of how different events you are hosting can help others.
Join other communities
Sometimes we get too comfortable within our own community that we forget there are people outside of it that could benefit from our events as well. Get out there and find other communities to be a part of: fitness clubs, social clubs, etc.
IMPORTANT: When you join a community, be intentional! Introduce yourself to others and establish genuine relationships with them.