If you're using Twitch or Picarto, you don't have to worry about your stream link changing between streams, so it's pretty easy to just make a post as you're setting up to stream and let people know you're starting soon. It's a good idea to have a "starting soon" screen in your streams and have that running before you post, otherwise people who click too quickly will think the stream either ended or got cancelled when they get there and see an offline channel. As for a tool to post stream links automatically when you start, I've not heard of any. Sounds pretty useful, though.

I use Youtube for my streams.

Ah, I see. Probably best you can do is start the stream with a welcome screen and then post the link here once you have it.