Facebook is a wonderful too given to us by God's common grace. I know for me it has been a joy connecting with fellow believers I have not seen in years and also with people in the city I live in. We know social media, not just Facebook, can affect us both positively and negatively, but they are useful.
One thing I like about Facebook is the ability to be part of Facebook groups. For those who are not aware of what these are, they are people on Facebook that become part of a collective (I know I am using a reference to the Borg on Star Trek) that share a common interest. For example, I am part of the Reformed Geek Culture. This is a group of men and women who are Calvinistic and love comic books, movies, video games, and anything else loved by geeks such as myself. I am friends on Facebook with some of the members of the group, but not all of them, which is one of the benefits of Facebook groups.
Another example is I am part of a Facebook group that is related to people in my neighborhood. This group promotes yard sales and even talks about issues in the city in a settle way without getting to hostile. This could also be a good resource for me to invite people to church especially to those I have not had a chance to meet in person.
The question I am addressing is should Christians be involved in Facebook groups. There is really no right or wrong answer to this. While it is great to connect with people, Christians and non-believers, who share a common interest with you, Facebook groups, like all social media should be approached with discernment and caution.
Is this a group where I am free to discuss topics or is this a group that only wants topics the administrators (admins in Facebook slang) want to address for their own ego? Am I joining this group because I have the same interests or just doing it because other friends are in it? Does this group allow me to engage in healthy relationships or unhealthy ones?
Here is one question we must ask ourselves, am I involved in too many Facebook groups? If you are, leave the ones you hardly post to or have no interest in. I went through that similar process myself as I went through Facebook groups that I don't engage in because I have don't have similar interest in. A few months back, I removed myself from a Facebook group because the group was becoming unhealthy in content and always like to play the "you are not reformed, if..." (I think you might have an idea which group I am addressing).
Social media is wonderful thing, but we must not abuse it just like anything else in this world God has given us.