They can't even block the site which provided you with the link because there are so many trivial ways to hide it - e.g. writing it as an image, or inserting it client side with some JS, or just encrypting it in an HTTP connect.
Given how popular a search app would be, it's likely that bittorrent clients would integrate with one. e.g. you paste a magnet, check the "web application" box, and perhaps the "keep updated" box and hit download. When the app downloads, the client hosts it through a http port so you can see it from a browser. Magnets are hashes so how the app is kept up to date is certainly an issue and also how it does its search, but neither is an insurmountable one.