I think it's possible to be comfortable as an introvert at almost any college. I certainly knew of many introverts when I went to college decades ago, and I matriculated at a place with a fairly big social scene. My freshman year roommate was introverted and did just fine. In fact, we became good friends. And I've often heard more current college students describe a peer or two as the type of individual wanting "to do their own thing" or "in their own world." I take that as somebody who is more introverted and less eager to jump in with the masses. The point is, I think there is room for all types in college. Unlike high school, college is a time and place where most feel freer to authentically be who they are. Many a student goes off to college with a desire to immerse themselves in deep academic study, and less the local social scene. Not everyone like to party. Not everyone is drawn to Greek life.
Despite the more accepting and even comfortable environment that the right college may offer you, I guess my question is are you just someone who is inherently shy, introverted and most happy to be on your own? Or do you suffer from some social fears and a lack of social confidence? It's possible that being introverted is a symptom of social anxiety or discomfort. Whatever the case may be, perhaps you should feel encouraged to spend time with a school or outside counselor who may help you learn some social tools. These might help you manage your natural proclivities and reduce any social anxieties as you head off to some inevitable social challenges and dynamics. It may even be helpful to role play simple ice-breakers. I suggest this because you are about to embark on a life-changing, new adventure. College offers you an opportunity for a fresh start and options to become a more engaged and social person than you were before.. From the way you ended your question, are there schools which will "help me become less introverted" my feeling is that you are looking to break out from yourself, and become more comfortable. Again, I would start with a professional, or your school counselor - supportive adults - who may help you prepare and arm you with strategies for social success at college. You need not feel as though you have to morph into someone who could run for class president. Even just a small change in your outlook and social confidence may make a big difference once you arrive on campus.
But back to the types of colleges you asked about. It may make sense to stay away from party schools. It's one thing to step out of your comfort zone, its quite another to step into a non-stop beer and vodka fest. I might also stay away from schools where Greek life dominates. At Georgia Tech, Greek like only represents about 25% of student life. That's a good mix for you. You might also want to seek out affinity groups and special clubs at college. There are religious ones like Hillel, sports ones, political ones - you name it. All may allow you to create a more intimate environment within a larger school. As for large versus small schools, although one of the experts above suggests large schools allow you to hide out and not feel compelled to join the social scene, really large schools can be alienating and overwhelming until you find your groove. Unless there is some unique feature about a large school that mitigates it's size, you may want to stick to more manageable numbers. And anyways, the point is not for you to hide out, but as you said, begin to become less introverted.
Most importantly, it may be helpful for you to consider the housing structure at a prospective college. At Yale University, undergraduate life revolves around it's residential college system. Students are required to stay in their residential colleges for both freshman and sophomore years. Many students have shared that this kind of housing system played a critical role in fostering a sense of belonging in the community.
Wherever you wind up, give careful thought to the culture of the school, and to the kinds of offerings and programs (residential, honors, clubs, research opportunities) that will provide you the foundation ad structure you need to feel as comfortable and as socially connected as you can. Best of luck!