Patent search for non-marketed inventions

Not at all - and quite to the contrary. What is the purpose of your search? Are you interested in obtaining patent protection yourself? Then you need to know if any patents have been granted or are pending as published applications, so as to determine what the probable patentability of your invention is. In a similar manner, are you intending to market your invention? If so, then you want to know if there are any patents or pending published applications where you may infringe one of the patents or the published application if the application eventually gets granted as a patent.