Inviting members into subgroups:
Existing Groupsite Members can be invited into a subgroup easily from within the 'Invite Members' area of subgroups by clicking the 'Groupsite Members' button at the top of the Invite Members page.
From that page, you are able to scroll through a list of current Groupsite members and select multiple members by holding down your 'ctrl' or 'apple' key while clicking on each members name. The invited member will not receive an email, but will be prompted with a pop-up the next time they visit the Groupsite asking them to accept of decline the invitation to the subgroup.
Non-Existing Groupsite Members can by invited into a subgroup from the 'Invite Members' area of subgroups, which defaults to the Non-Members invitation page. New members can be invited into the subgroup, but must first join the overall Groupsite. Upon joining the Groupsite, they will be prompted with the join subgroup pop-up. (Note: Invite premissions for subgroups follow the overall invite new members permission settings for Groupsites. Hence, if you do not have premissions to invite non-Groupsite members into the Groupsite, you will not have permission to invite them into a subgroup within.)
Here's a quick video that shows you how:
How To Invite Someone into a Subgroup from Shaun Callahan on Vimeo.
Subgroup Invitation Reminders
After closing the pop-up window, a member will see a Subgroup invitation reminder re-appear when he or she visits another page in that Groupsite page.
If a member chooses the "Remind Me Later" option in their Subgroup invitation, the subgroup invitation reminder will re-appear to the member 48 hours later. The member does need to be logged-in to their Groupsite to receive the subgroup invitation reminder.
Choosing Groupsite plans that allow managers to directly assign members and prospective members into subgroups eliminates the need for subgroup invitations and pop-up reminders. The ability to assign members into subgroups is available in Large Plans and above (or, if you are in a grandfathered plan, the Midsize Groupsite Pro plans and larger).