Android iGap makes it possible to do many activities in your channels. As you know you can add members to your own channels and/or the members join the public channels themselves, you can send your channel address as an invitation link to make other members maybe in your private channel join it simultaneously and increase the number of members all at once.
In the Web version iGap you are able to have groups in private and/or public. To add more members to a public group needs the group address. It is effective to use the @ at the beginning of the group username and send it as an invitation link to a private group to invite members and make members of your public group more and more.