I actually was limited by Facebook just for trying to find the beginning of a relatives' public timeline. Flagged and limited for suspicious activity. Ridiculous.
I will suggest ninja planner as a good facebook group finder. I think Mass planner is not working anymore. So, you can try this one for yourself.
Mass Planner is discontinued.
All the tools are not provide correct data you should find manually facebook group:
Search for relevant groups
Log into your Facebook profile.
Enter a relevant keyword in the search box at the top left of the page.
Click the Groups tab to see a list of groups related to your search term.
As above, click on the name of the group to learn more, or click Join to become a member.