I think it's because you haven't been scouted yet, so your art doesn't show up in public listings, only on your profile. More info on how scouting works: http://ornery.newgrounds.com/news/post/388624
Maybe there's another way to participate, other than the tag? Could you send him a message, or leave a link on the contest post, or something like that..? A lot of new users aren't scouted, so there should be a way.
Cyberdevil
Hey there Zelvica993! Welcome to the site, and good luck on the contest!
Zelvica993
Hey! Thank you. Maybe you could help me? I tagged the picture I made for that contest but when i search the tag my entry isn't there. Even when I log out of newgrounds it still isn't there. Do you by chance know why? I really want to be in the contest and I worked hard on it. But every time I search b-pokemashupchallenge my entry doesn't show