As someone who is also somewhat "introverted" and spend most of his time indoors just playing some games and watching some tvshows/anime, what made me go outside was an outgoing person who was willing to drag me out of my comfort zone. :)
At first, I honestly don't like it as I was not used being under the sun and even walking places (going around the mall is tiring). But over time, I kind of long it. I think what you really need is a person willing to teach you the world outside your room. :)
What you need is to invite friends in first. Let them fill you and your room with energy. Then when you start enjoying it, they leave. This will make you long for it, miss it and eventually crave it. Then you see them flexing outside and you want it too. So you take those baby steps out of your room and into the world.
Do you like being outside at all? Or think you might be open to it? I've found, at times when it's hard to get myself out of the house, as soon as I do I actually enjoy it very much and end up spending much more time out of the house than I had intended to. Sometimes all it takes is the initial process of walking out the door.
For instance, although I greatly prefer to make coffee at home, I've often made it a habit to go to a local place that's deserving of support to fill my mug rather than just making it at home. Financially, it's pretty stupid. But it does make me leave the house as I usually want that coffee pretty first thing. Usually the thought of it is dreadful, but then when I actually embark on the mission I really enjoy it! I often will end up extending my coffee outing long after I had planned on returning.
I guess all I'm trying to say is you gotta find something to get you outta the house. I lived with a bunch of kids I didn't know and who were pretty anti-social this summer and a lot of my friends had moved out of town. I hated going "out" and socializing with random people but then a bar/arcade opened and I started to go there every day. It was like a compromise to me- I was around people and would occasionally find myself in conversation; but I could also just play video games and drink a few cheap beers.