I loathe the term networking. Not as much as “synergy” mind but it’s close. Yet the activity itself is vital to a scientific career and the shortest path for most of us to breathing into a paper bag.
Bob Williams, our Bullitt Lecturer had some interesting insights into the social mechanisms of science. He was adamant that a personal interaction is the gold standard. One-on-one science discussion and interaction. I agree. But he also correctly identified that this has a ludicrous onus on people and (thanks to airmiles travelled) environment.
So how to supplement or replace it? I suspect supplement. I use Twitter in part for this. Engage in new things that people have done is okay but it lacks a little in depth of interaction. A big plus can be that you had a mild interaction over Twitter and so IRL introductions become a little lower threshold? On the downside, friend-on-Twitter is less familiar than people (e.g. me) tend to think.
Like most astronomers of his generation you can best reach Bob best via email. Something he checks and responds to religiously. But that is hardly true for more recent generations (ahem eg students). Skype or google hangout or Zoom can certainly replace a lot. Especially for committee meetings for example.
So interact initially in person and keep up and active over electronic means as may be appropriate. Vague but then again it’ll be different person to person. In academia, no one checks linkedin, but outside it's a vital tool. You may even have to pickup the phone, dial the number and talk that way.
The issue remains unresolved. In part because science is a mix of personal and generational preferences in communication. Key remains to take initiative. Junior people to contact the expert they want to talk to.