Maybe it's just the people I have added on LinkedIn but it always strikes me as a very superficial place and not the one for deeper connections or discussions about projects. Twitter on the other side seems to be more promising (at least in my case).
While my posting cadence of "something interesting" every few months works well for Reddit, that's not something that gets people to follow and engage with you on Twitter.
In my case, doing nonprofit/volunteer work has been a great place to make new friends (and the occasional enemy).
Sadly not interested in nonprofit volunteering at the moment, too worried just making ends meet. London’s very expensive these days and wages aren't great.
After you built up a few interesting accounts finding more accounts via Twitter is easier and less noisy.
I think there may be other places with a higher density of very specific purpose, like angel.co
edit: this point is made in the article - "The beginners guides to everything have already been written. What’s missing is more advanced content."
I guess the specificity of the discussion is the main thing interesting there, provided startups are your thing.
For other things, hobbies etc., there may be more specific places where you get a concentration of focused discussion on a topic.
If you want to find friends (not just potential business associates), I suggest trying to find some other personal interest of yours that isn't money-related. Perhaps sharing on a different platform as well.
It's these kind of topics that I enjoy talking to people about though. I get very quickly bored if we talk about other stuff. Sad I know.