Assume it does. Even if it doesn't, it will.
How can you find out if your idea already exists? GOOGLE IT If you are planning to launch a product, you should have a lot of information about that product. You should already know at least some of the keywords you would use, product descriptions, potential buyers, etc. Use those pieces of information to search Google.
Step 1) Find potential customers for your product (note: this should nearly always be step one).
Step 2) Ask them (then take that opportunity to tell them about your idea and see how they react).
Then of course there's always the obvious stuff, like Googling and searching Crunchbase.
Surprised to see nobody has recommended CrunchBase yet. For a new idea of mine I Googled and came up with nothing after countless hours searching. I looked on CrunchBase and discovered a similar startup with poor execution.
For some reason a lot of people seem to think that because it hasn't been around that long, it's no use. But trust me, there are thousands of companies in a wide variety of niches and my idea is something I think is pretty unique and not many people have thought about, hence only finding one bad competitor I plan to maim shortly.
CrunchBase is definitely something you want to consider when determining if a startup exists. Not to mention it gives you info pertaining to any venture capital the startup might have raised and a few other goodies.
I am sure you already have done the basic... searching on Google. If you have not, then start there, chances are the product or service you are trying to build already exists in some way or another. If it doesn't, then you either have a very cool new idea, or there is just not a market for it.
This is going to be a shock: You don't even need to look if someone already implemented your idea. If your idea is good, other five people in the world are working right now on it. If its very good, other fifteen.
No one is so unique to be able to think in something 100% original. The exceptions are ideas far ahead from the market (like tablets, 10 years ago) or with a poor market target (in size or in wealth or in both).