The problem with most non-profit attempts at creating a community is they focus on the end goal.
The power of being part of a group that does good is greater than the power of simply doing something good. Donating money temporarily makes the guilt go away. Participating in a group that raises money (and awareness) gives meaning and purpose to life. It’s a bigger motivator than simply giving and going.
In short, it's less about what you’re trying to achieve and more about who you’re trying to achieve it with.
The big opportunity for non-profits, and many other organizations, is to focus on the with part of the process. Milestones are great, but who and what people are doing is better. Who has joined the group this week? What do they like/enjoy? What events are coming up? What is your group challenging each other to achieve this week?
Write more content about the people in the group and ensure that discussions give plenty of opportunities for people to give opinions and go as off-topic as they please. Ask questions all members can answer. Go beyond raising money and make sure you have a group that genuinely cares about each other.
You want people to join a group that raises money, not make single donations.