Do you have any work to give to people that want to help you?
Non-profits are big culprits. They gather a large community of people eager to help, then only ask small things. Donate $10. Tell your friends. Write a letter to your local politician.
People want to do more than that. They want to use their web-design skills to help build your site. They want to use their marketing skills to assist you with your campaign decisions. They want to use their journalism skills to help write content for you.
I’d happy offer some community consulting to organizations I liked. But none have a means for that. Not a single community of which I’m a member, nor any company I really admire, has a volunteer your skills area.
Create a program for people that want to help you. Put together a brief list of tasks that need doing. Let people register their skills and their time. Let the group self-organize as much as possible, you help co-ordinate and motivate.
You might find that a) the results are impressive b) recruiting becomes easier and c) the people that help become even more loyal and and evangelistic about your organization.