They released the list, Here is the list in full!
1. Avril Lavigne
2. Joss Stone
3. Jesse McCartney
4. Omarion
5. JD Natasha
6. Hilary Duff
7. Blaine Larsen
8. Ashlee Simpson
9. JoJo
10. Mario
11. Ciara
12. Brie Larsen
13. Raven
14. Brooke Valentine
15. Trey Songz
16. Fan_3
17. Fantasia
18. Smoosh
19. Kyle Riabko
20. Lalaine
21. Lindsay Lohan
http://music.channel.aol.com/feature/21under21