In order to add any members to a group you must first of all be a member of the group and friends with the person that your trying to add. Adding a few people to a group is no problem by hand but adding large amounts is a time consuming job.
I have for that past year been using a tool that add friends to my groups very quickly. The software will get you restricted from adding members if you use it too much but the restrictions that you will receive are not to long and I always use these times to get more friends to add once the restriction is over.
You can access the google chrome plugin and install it for free from clicking the link below
Once the plugin is installed you simply open the page of your facebook group that you wish to add to and then click the new Green button at the top of the screen in the address bar. The plugin will then start to very quickly add your friends to your group. The extension has been programmed according to the current adding rules and adding up to 900 members is normally about the limit.
No need to stop the extension while its working, it is set to automatically stop when it gets to the limit. It may run a little bit over or under as the limit is changing all the time. But you can safely add up to 900 people and only get a short ban.
Unfortunately not getting banned is not an option for serious group developers but the bans are short lived and the extension is also very clever in the fact that it will always try not to add the same people that it added the last time that you used it meaning that the extension is the best available at the moment.
This is a very fast and powerful way to add people to your group. It is a good free Facebook group members adder software that you can use to grow your group.