I want to tackle this question more directly from the "Intorvert" angle. In my case, I'm using "Intorvert" as a term to mean someone who gets physically and mentally exhausted while engaging in a social atmosphere, and needs time alone to recharge. While there are additional classic introvert tendencies, this is the only one I consider relevant to this question.
For me, the denser the crowd, the more drained I'll become. So while an organized, open layout like a theme park is something I can enjoy all day (before needing a full day to recharge afterwards), a densely packed ballroom at a company event will drain my batteries in well under an hour. As a general rule, the more comfortable I am with the people around me, the slower it will drain, but I'll still vote for "parties" of four or five friends rather than ten or twenty. I'm not shy, I love performing in front of a crowd, and I don't have anxiety issues - but I still opt out of company events when I determine it probably won't affect my social standing.
So... there's the real question. How do you determine if it will affect your social standing?
First, IT_Guy, I'd like to applaud you for going to one of these events when you first started working at this job! For an Introvert, just the description of the event likely made you assume it wouldn't be your cup of tea, but you went anyways. This is important when joining a new job, because it establishes that you're a team player.
Which brings me to my first bit of advice -- despite the fact that you're in the same Company, since you're in a new team, who doesn't really know you yet, you should treat it as a new job and attend the event once. Yes, it will be exhausting, and you've already established that you probably won't enjoy it, but your coworkers will remember.
After you've attended once, your obligation to this particular party has probably been fulfilled. When you decide not to attend, I suggest being honest with your coworkers.
- "I'm going to pass -- I've been before, but it's not my cup of tea."
- "No thanks. I went once, but it was exhausting; I'd rather stay here and work." This is meant as a joke; do not feel compelled to work overtime
Chances are, if your coworkers are observant, they will have noticed this (mine usually laugh and nod to themselves). However, there is still a possibility of affecting your social standing - in order to minimize any negative affect, make it clear that you're rejecting the event, and not the opportunity to spend time with them. Tacking on something like "But let me know next time you go to grab lunch!" establishes that you want to be included in the team.
If there's ever an event that includes just your team, and not the rest of the organization? Suck it up and go. Even if it's not explicitly labelled as team-building, it probably is. You may not like them all, but getting along with them outside of work has the added bonus of making them more likely to be more responsive or helpful during work hours.
Finally, I've seen a few suggestions that not attending company functions could hurt your career path - and my personal counterargument is that I wouldn't want a promotion that required me to attend monthly company parties. Earn the promotions you get from working hard and being a great team player, and if this particular company doesn't recognize those efforts, find a different one which will.