File Search Engine

I would like to create a file search engine script like, or
But i dont know how this type of sites populate their databases with files.
Searching google a list of keywords with proxy and adding the file links to the db, sounds complicated and unpractical.
First it will be a strugle to get fresh proxyes daily, and also have problems with google banning me for too many queries.
There are many such sites online but i dont know exactly how they work or what scripts they are using.
Some help would be apreciated.