Starting from version 1.7.1 there is a new function in GroupSo to invite members to a group.
After creating a group (see related articles) there is a new option called "invite".
When pressing that button a list of users pops up with a search function so you can start inviting users to your group.
For people who receive an invitation they got 2 options when going to the group: "Accept" and "Reject".
A great new feature and easy to use so let's grow your groups!