It helps to understand how torrents work.

A torrent file is basically a map that points you to other users who have part or all of a file. When you download a file from a torrent, you are downloading directly from the other users.

The website that you are referring to is called a tracker. It hosts torrent files, but not the files themselves. Basically, it hands you a map and tells you to find the file on your own. The tracker does not directly interact with the pirated material. It only points users towards it. Because of this setup, it is extremely difficult or impossible (depending on your location and the tracker's location) to prosecute them.

Your best course of action is to download the torrent yourself. Once you are connected to a torrent, you are able to see the IP addresses of every other user who is connected to it. Track these IPs and report the users to their ISPs.