alt Hacker NewsIt probably depend on where you live and who you are. LinkedIn is my backup in case of a layoff. It's the site where I can reach everyone who worked with me or have made offers in the past.
If you do what I do, live in my general area and know the right people (which I do), LinkedIn will get you an interview or three lined up in a day or two. None of these people are on Indeed, HackerNews or even Slack.
I think before linkedin people were doing this with email and phone. Literally cold calling your old coworkers. Not sure linkedin really created anything that didn’t exist previously especially if you live in some major hub of industry as you indicate.