How to Find Groups With the Largest Numbers on Facebook
Facebook Groups are community pages where Facebook users united by common causes or interest come together to post and discuss the topic of the group. The larger a group, the more prevalent and frequent interaction occurs within it. Find Facebook Groups with the largest numbers of members to maximize the number of people with common interests with whom you interact.
Log in to Facebook. Type the name of the topic for which you want to find a group into the Facebook "Search" field. Don't hit "Enter." Rather, click "See More Results."
Choose "Groups" from the list of filters that run along the left side of the results screen. Scroll through the results until you find the one with the largest number of members. Member count displays within search results.
Click the name of the group with the largest number of members. Inspect the group's page to see if it interests you, then click "Join" to join it.