At least in my experience, my solution to this was forcing myself out there. I started taking little steps, such as going to festivals on my own. I would set goals to try to talk to at least one or two different people (Pokemon Go really helps me with the whole getting out thing). It was really a struggle, but it's helped me be more outgoing. I am still very skittish and sometimes get very bogged down with the loneliness, but I'm in a much better place now.

Do you have any hobbies? You could use this to gradually work your way into meeting more like-minded people.