You can always leave a group and return at a later date. What you want to avoid is joining 10 groups and getting overwhelmed by all the activities. Try just one or two at a time, stay with the ones you like, and move on to check out others.
When it comes to finding a group for learning social media, you're going to go outside your business interests. At the top left of the Meetup site are two links. One says "Find a Meetup Group" and the other says "Start a Meetup Group." We'll leave starting a group for another article.
To find a group that will help you learn about social media, you can always type "social media" into the search box. That will get you lots of results.
My suggestion is that you narrow it down by searching for groups of copywriters, site designers, marketing and advertising professionals, or media consultants. One type of group you should avoid is MLM or Network Marketing. It isn't that these are bad groups — quite the opposite, actually. It's just that their focus is quite narrow, and you'll spend a lot of time fending off recruiters.
In my experience, people in my profession are quite willing to answer your questions. We'll spend time with you at an event - especially if answering your question draws a crowd. You can usually even get 30 minutes to an hour for free after the event.
You'll probably even find someone you can work with to develop a social media marketing plan. That will give you the help you need to combine your current traditional advertising with social media — just like you're doing with Meetup.