Welcome to VATSIM! Can you clarify what you mean by "join this VATSIM group"?
You're posting on VATUSA, which is a group of over 19,000 active pilots and over 1,000 active controllers and ATC students. Each of our ATC facilities hosts its own TeamSpeak, most of the TeamSpeaks are dedicated to controlling (though one, two or a few openly welcome pilots as well). Most pilots on VATSIM don't connect to a TeamSpeak. Some join a virtual airline and most of those VAs host their own TeamSpeaks.
Maybe we just need a bit more clarification of what you're looking for to better be able to answer your question.
In terms of who you see, a lot of that depends on day and time of day. Weekends and weeknight evenings tend to be busier in the USA. Suggest you use a program like VATSpy or AccuMap, or view
www.vattastic.com, to aid in situational awareness to see who is/how many are where.