Not many groups offer a sense of belonging. Most groups don’t try. Members join for a tangible benefit rather than an emotional need. When a member really feels they belong amongst a group, the loyalty, commitment and willingness to help increase dramatically. You have them for life.
Creating a sense of belonging requires a high-involvement approach. Far higher than you’re currently doing. Every member needs to be treated as an individual. S/he needs to be personally welcomed by others, invited to get involved, given responsibilities, have a mentor/buddy to see them through and sought out if they’ve gone absent for a while.
Most organizations, including yours, will say a super-high involvement strategy isn’t possible. It requires too much time, money and resources. It is possible, just not if it’s entirely run by your organization. You need every member to help run the community.
Most branded communities move too fast. First they try to get a lot of people, then they aim for a lot of involvement. Do the opposite. First try to get a lot of involvement from a dozen members, then grow steadily. Never accept a member if you can’t offer a high-level of contact. This is the level of involvement you should strive to achieve. You want members to feel you care about each person.
A high involvement strategy should, naturally, get members more involved. If you begin high-involvement from the beginning, it ripples onwards throughout the community. Every member will be involved.
If you already have a community then begin a high-involvement approach with just 10 members. Contact them often, both online/offline, solicit their views often. Highlight places they might like to participate. Offer them roles and responsibilities. Spend 80% of your time on just 10 members. Soon they should do the same with 10 of their own.