You might ask your audience to follow you on multiple social platforms.
The goal, I suppose, is to have another channel to distribute information and guide people back to the community.
How about trying something different?
Instead of asking people to follow your brand, ask them to follow each other.
More specifically, create a list of the top 5 to 10 members in your community (especially those that use their accounts to discuss the topic) and invite newcomers/existing members to follow them instead.
It rewards the top members and provides newcomers with recommendations of who the experts are.
You don’t need the group to become bigger, you need the group to become tighter.