Thank you for the answers.They were all very helpful!
I think crowdfunding is a great approach but not an option for
me.At least for now.
What i mean is that i just have an idea not a well thought project
so i am not in a position to set a target to be met through
bitcoincoinstarter.
The best case for me right now is to find a partner (that can finance
a project) and create a business plan together.
What do you think?
Well I guess finding a partner would involve disclosing details of your idea in order to get people interested. No way around that. I am not sure what the best place for that is though.
I think if it is more about finding a partner for the financial part of the project (someone that has knowledge about company founding in your country and the economics side of things) you should seek for internet forums in your country for such poele (sorrry I have no idea where t find such forums). If you are looking for a partner for the actual development of the game places like the already mentioned OpenGameArt.org or other websites that revolve around gamedevelopment would be a good start. Again it allways will involve sharing at least parts of your idea rather public in order to get people interested.
But apart from that: In my view making a business plan is not all that hard. Since you are planning to make it a webbased game you'll need a server. So inform yourself what the prices at different server hosting companies are to get an idea of the costs for that. Approach some artists and ask them what they'd charge to provide art for your game. If you are not a coder yourself also approach some game programmers to ask what they'd take per hour to work on the project. All this makes up your cost and gives you an idea of how much money you need to make from the game to break even and start making profits. This will in turn help you to determine what business model for the game is able to work (subscription, buy to play, free to play with microtransaction, funded through advertisement).
In all fairness i have to say that all of the above is just guesswork based on common sense. I've never founded a company nor did I ever created a complete game. But this is how I'd approach such an undertaking.