Which social media platform is best to use for free trading signals?

I used to run a signal service a couple months back. Started off with twitter.

The problem with twitter is it is kind of too public. The advantage is it has a wider reach. I eventually switched to telegram, where I can control things better, set basic rules and have a bot take care of things in my absence.

I wouldn't really recommend facebook. It doesn't seem like the right platform for it. Best choice, use telegram

You can use Telegram. However, Twitter has some good signals sometimes, but it is always best to follow traders that you know and trust. 

The added benefit to Twitter is you can see when people are writing off their trade ideas - things that should be avoided at all costs!