Have you visited a forum and noticed empty sections for redundant or non-existant groups? This is the result of a top-down strategy. The community manager created these forums before they were needed, and they're still not needed.
Many community managers make this mistake. They create separate groups/forums/pages within their community in advance. This usually results in 2 – 3 overused forums and 10 underused forums.
Take a bottom up approach instead.
The best communities are often filled with forums and groups with names and topics that make no sense to newcomers. “The 3am insomniacs club”, “Mike and Joe’s freeze-flower forum". “No shoes in here”.
This happens when you recognise growing topics/friendship groups in your community and creating a place for them. The members sets the name, they get to control it, they get to moderate it. This is a bottom up strategy and it's by far the best approach. You create a new forum when your community needs one.
Develop a strategy to recognise when friendship groups are forming. Have an approach ready for these groups. Then offer to create a place just for them within the community. You should never have an unused section of your forum.