How do I avoid these company outings without feeling like I'm an outcast?
... you can't.
People form friendships at things like that. It's the same as if you join any organization, then refuse to eat lunch, take smoke breaks, or spend time with coworkers outside of work. It is natural when a group participates in these and one person does not, the other person will feel like an outsider.
This can influence your work interactions the same way posting negative things on Facebook can. Is either situation fair? Probably not. But part of how social humans work.
Now, there are two situations here.
1. Friendly teasing
If this is the case, I'd just get used to it and realize you are going to have to, if you want to keep not attending those events. If it's friendly banter, not a big deal.
2. Serious frustration
It may be your coworkers legitimately feel as though you don't want to be part of their group. This might make them feel as though you think something like, "I'm too good for your group." Which, somewhat is true, given what you said about preferring to spend time with your friends instead.
In this case you probably can't just ignore it. You can find time to spend with them though in similar contexts. Perhaps lunch, or a morning "how was your weekend?" conversation. Maybe try to find some time once a month go to one of the events. You might not be connecting as much as they are but they at least see you putting effort into the friendship/team camaraderie. This can greatly help to avoid them feeling like you don't care or are too good for them.
By the way, I have similar issues given where I live (25 miles in wrong direction of 99% of my coworkers). I make efforts to eat lunch with people or connect when I can because I do not have the ability to spend time with them outside work, without serious effort on my part.