I'm pretty introverted. I don't feel lonely when I'm home alone with my cats. I don't feel lonely in the sense of lacking conversation with someone. Over the last year or two, I've done a lot more hiking and spending time outdoors. I've talked about it on Hubski a fair bit, and I really like it. But as I daydream about doing more, taking on more challenging climbs and longer backpacking trips, it feels really lonely. I wish I had someone to do it with. I do have my core group of friends, but they're mostly music friends, not "spend a few days pushing yourself to the ragged edge" friends. Some of what I want to do starts to border on unsafe alone. Avalanche risk or an uncontrolled decent is a real problem. It's lonely. I signed back up on a dating site (lil) and messaged a couple people who had profile pictures of them in the woods rather than holding a beer at a football game, but I've made no progress.
The introvert kicks in then. Hiking is only so-so popular locally, so I have to travel a bit. But point taken; I'll try to make an effort to find meetups both locally and where I travel.
From one introvert to another: don't let your fears drown your self. It's hard to meet new people, but don't let your mind lead you by the idea that it's bad just because you're afraid of it. In fact, from what I've learned so far, it's best to do what you're afraid of and persevere through fear; resilience, it appears, is a mental muscle which is ought to be flexed if one wishes to remain resilient.