How do you discuss interesting research online?

Suppose you find a nice, interesting research paper online somewhere (say arxiv) and you’d love to find other people who read the same paper to discuss it a bit (even if briefly). Maybe you want to share a flaw you found, or maybe it made you think of a new idea, or you want to talk about its interesting use of methods, or even advertise that you did something similar. How would you do that nowadays?

I expect answers such as: my own research group (too limited/potential echo chamber); researchgate (too ”social network” for my taste, no focus, bloated interface); twitter (not even sure where to start?).

Any other ideas?