Okay, I don't think this is the answer, but it seems to fit.
You are:
A web ad --like Google AdWords
Explanation:
I'll use Google AdWords for the following breakdown for example.
I am being sold by somebody that didn't find me.
Google is selling ranked results for companies' products to show up at the top of an individual's Google search --based on the words used in the search. Google is selling it, but didn't "find" it --the person surfing the web did.
The finder did not create me.
The customer/person surfing the web using the Google search engine finds the Google Ad result at the top of the result list, but Google created it, not the person surfing the web.
The creator did not know I was created.
This part is possibly debatable depending on how you view it, but Google didn't necessarily know the add was created as it is automatically created for the client. It does however track the clicks that the ad generates and charges business that is paying for the AdWord result.
Perspective dictates my value.
The value of the AdWord is based entirely on the perspective of the customer --how interested the customer is in the product to click on the ad.
What am I?
A Google AdWord --Or any other web ad provider that potentially works in a similar way. This is just the only one that I am familiar with.