I do read a lot of forum posts, reddit posts and other social media posts in my spare time, and about once a week there is someone spouting an idea that they have, and wish to pursue.
These people won't come out and say what the idea is as they are afraid that someone will 'steal' it. Which simply doesn't happen.
Well guess what? I have over 600 ideas for comics and/or games written down.
I have folders full of these ideas, I have bought scrapbooks specifically for jotting down ideas which has filled binders with loose pages of ideas. They might be ideas for a game, or for a comic book, or for a book I might wish to write someday.
At the end of the day though 95% of what I write is never going to be made into a project. The trick is to pull the pin on an idea as soon as you realise that it isn't going to work; the quicker you can make that decision then the quicker you can get onto your next project.
Don't ever beleive the hype that 'Winners never Quit', they do and quite often. When a winner realises that he's not on the winning track then he will stop and move on.
You need to realise that there is no 'bad' time to stop a project once you can see the writing on the wall.
I've personally woken up, and read an idea that I wrote the previous night, and nearly slapped myself for having such a stupid idea; I've build prototypes of games and then realised that the key mechanism simply doesn't work; I've had games ready for the polish stage but then found a competitor that did everything my game did but better (can't believe I missed that competitor in the research phase).
Whenever I read a post from someone with the 'next best idea' I roll my eyes and move on; I used to comment to let the person down slowly but now it's got to the stage where I don't even reply.
I thought it was just me until I read a rule on a sub reddit which put it a lot more bluntly than I ever would, the rule was that if you had an idea that you could "F*** off and take your idea with you". As an Australian I'm usually blunt and too the point, and even that comment took me by suprise; I mean, that's what I was thinking but I would never write it!!
The rule that tells you to "F off" with your idea did go into more detail, they explained that everyone has ideas but they need to be developed before you can ask for help. Don't just say "I have an idea for a Zombie apocalypse while Aliens steal our drinking water" and then ask for someone to write the script; you need much more info than that before you can ask for help, and usually you need to have a first draft of your script!
Oh, and for humanities sake, don't ask people to help you for free as what you are doing is asking for people to help you make your 'fortune' while they get no rewards. "Split future profits?", you sound like an idiot if you offer this if you put nothing up front, so don't offer.
"Splitting kickstarter revenue"? - dubious; kickstarter campaigns are notorious for mis-judging all expenses, so you may offer "20% of revenue for the artist" only to find out that you don't atually have any money left after printing, and postage, expenses.
Have ideas ever been stolen? Depends on your point of view. Considering doom was the first "First player shoot 'em up" then you could argue that every other game that followed (including Overwatch, Battlefront e.t.c) was 'stolen'.
In reality nobody ever reads 'ideas' reddit posts (yes, they exist) and uses that idea verbatim; if anyone can point me to any game that was made purely on an idea post I would love to see it.
I spent about 10 minutes reading this ideas post and 90% of them had already been made (the idea added a minor variation); Some of them were just wierd ("A first player shooter in a Jungle that uses spear guns!"); while the rest could be considered complete nonsense ("A city building simulation where, at any moment, you could take over one of the inhabitants and walk around like a first player shooter").
If you do have an idea and someone runs with it then don't expect to be financially compensated for it. If you give me a 2 sentance idea for a comic story and I spend 20 hours writing it into a full script then pay an artist, who spends 100 hours on it, then we get the financial rewards - not the person who spent 30 seconds coming up with an off the cuff idea.