If I had to spend that much time writing messages, I'd rather just volunteer my time at a non-profit, join a club, or attend some sort of meetup.com meetup to get to know people in my neighbourhood and/or within my city.
When you join an organization based around something, you can be pretty sure that most of its members will share at least that common interest with you. But how do you find the organization in the first place?
If you're anything like me, you probably end up trying out a bunch of potential hobbies before you find one you stick with. When I was in grade school, I tried gymnastics, figure skating, soccer, basketball, violin, clarinet, viola, guitar, math team, Magic: the Gathering, Starcraft, a brief flirtation with policy debate, and probably several hobbies I can't remember now. The only ones I really stuck with and made friends through were violin, guitar, and M:tG. When I was in college, I tried orchestra, the Arts theme house, Taiko, whitewater kayaking, bridge, sailing, theater, improv comedy, Woodsy club, etc. The ones I stuck with were orchestra and sailing.
It's easier to do it this way if you're afraid of rejection, because you're rejecting an activity instead of rejecting (or being rejected by) a person. But it's no less time-consuming. You have to reject fewer entities, but it takes you longer to decide that you don't actually want to pursue that line, so it ends up being pretty much a wash.
It comes down to wanting social interactions without having to go through that small talk stuff that most people need to go through in real life.
I also do volunteer my time as well. Although I do understand concern for making the best use of one's time. I only messaged people whom I felt there was potential.
The same filtering applies though because you can attend things where there aren't many people you could relate to or you can only relate with that one particular interest and nothing else.
"Hi, so what's your favorite album by [music artist]? Mine is probably _____. Have you been catching up on how Barcelona is doing? I also like the Matrix movie. If you were in Neo's position, would you choose the red or blue pill? I would probably pick blah blah because blah blah.
-Matt"