Code design to make adding similar tasks later easy

For example I have a app that can download videos. Since the tasks for downloading are similar I create a base class for downloading.

public abstract class Download {
  public abstract void run();
}

For each concrete website, where videos can be downloaded I create a child class from the base class:

public class DownloadYouTube extends Download {
  public void run() {
  }
}

public class DownloadVimeo() extends Download {
  public void run() {
  }
}

To see from which site the user wants to download I create a enum and switch through it to create the right object, then I call the common method run().

public enum WEBSITE {
  YOUTUBE,
  VIMEO
}

public void startDownload(WEBSITE website) {
  Download download;
  switch (website) {
    case YOUTUBE:
      download = new DownloadYoutube();
      break;
    case VIMEO:
      download = new DownloadVimeo();
      break;
  }
  download.run();
}

Later other people may want to add new websites. With that design it is not to easy. People have to edit on three places: They have to alter the enum, they have to add a new case and they have to write the class itself.

It would be way better if the had just to write the class.

Is there any common code design or other advise to handle such a situation better than this?