There are a seemingly infinite number of groups you can join on Facebook, but if you're focused on growing your career, you'll want to stick to public or closed groups related to your industry. With public groups, you can join with the click of a button, while with closed groups, you will need to request an invite before joining.
Try out various search terms, like technology and your city, or industry-specific technology terms. You'll see a list of all the groups matching your search terms, how many members they have and whether the group is public or closed. Entering terms like "women in tech," or "Boston developers," and filtering by groups will bring up a number of options. Some are well-established, but you'll also find a bunch of groups that seem abandoned or defunct. Before you join a group, take some time to scan the page to make sure you're interested in the type of content they share and the type of interactions they have. It's also a good idea to make sure the group is currently active, with people posting as recently as one week.
Once you find interesting groups that you think might help grow your career or network, go ahead and introduce yourself. It's a great environment to informally meet new people, and it these online connections might turn into valuable in-person professional connections down the road. Since the group you join will ideally have a strong focus on your industry, you'll know everyone is in it for the same reasons as you.
Try posting a new message that tells people about your experience in the industry and what you're looking to get from the group. Find other recent posts that you can respond to in order to show the other members you're invested in the group. Connections are vital to nearly every career, especially in tech, so it's time to embrace your online network as much as your in-person network, and Facebook is a great place to start.
You don't want to join a group only to be inundated with notifications day in and out; it's enough to make you ignore or leave the group just as fast as you joined. Facebook actually gives you a lot of control over the notifications you receive, so it's a good idea to adjust the notification settings within the group. The upside of Facebook over LinkedIn, is that Facebook doesn't send out newsletters regularly, whereas if you join a LinkedIn group you'll find "group digest emails" stacking up in your inbox. You can control these notifications, just like on Facebook, but it's one less thing you have to consider if you join a Facebook group versus a LinkedIn group.