Community Engagement is partly marketing, but it is much more than that. Marketing of a nonprofit is a very different activity than marketing to sell a product in spite of some similarities. Every facet of the organization has to be involved to be effective.
Resources
A set of annotated links on Community Engagement (as well as other topics, that will be linked elsewhere). They include materials on how to engage the staff, Board, clients, members and supporters in increasing the visibility of your organization and its mission in the broader community. (Creating the Future, a nonprofit in Tucson, AZ)
Another set of annotated links on Community Engagement, including advocacy communication, advocacy planning, community engagement, lobbying, and political activities and public policy, from a site with a wider array of offerings that are listed under other topics as well. (Nonprofit and Philanthropy Good Practice site of the Johnson Center at Grand Valley State University)
Nonprofit Alliance at Kellogg Community College has a list of links to resources on other sites.