Discuss Small Group Models
I'm leading a closed small group and I'm afraid that we've become inward focused. How can I help my group reach out?
In my experience with 'closed' small groups, the reason we were 'closed' was to provide a safe context for mutual growth and accountability. And we limited our numbers to not more than 8 members. The danger of becoming 'in-grown' in an unhealthy way was resisted by setting a time period for the life of the group, usually a two year maximum (though one went an extra year), upon the conclusion of which our declared intention from the beginning was to break up, with members forming new groups with new members. This worked well for us. (Past tense because now in a new location with different approach so far to small groups.)
Even in a closed group, you can challenge one another to "practice" one's faith by taking on a service or mission project, as mentioned in a previous post. Challenge the group to "step out of its comfort zone" by doing something that requires more than they've done before. This will unify the group but also provide new experiences to share and discuss in future sessions.
How about splitting your group? Then your group can start inviting new members and the new group can also invite new members.
Spend some time focusing outward. Get your group involved in a community/missions/benefit project. Do something as a group that both binds you together as Christians and points your focus towards our broken world. Maybe even consider joining forces with another small group to complete your task.
As Harry said, The goal of an "Open" group is to continually add new members to the group. So if you want it is better to open your group.