A few resources for film competitions (search High School):
Film Freeway Film Festival Search
Withoutabox Film Festival Search
Current Philadelphia film competitions:
On Vimeo you can include your video in Collections to increase the potential viewership. It is also very important to choose a captivating thumbnail for your video. This can be selected from your film in Vimeo, or you can design your own still in Photoshop or Illustrator. Including your title in the image can be helpful.
Vimeo Staff Picks is a good place to see examples of thumbnails that work well, as well as high quality films and animations