We do not have a teen volunteer of the year.  My personal pref. is to celebrate them individually for tasks or actions they do over or beyond - just something little. 

We have teen volunteers year round, but do have 4-5x as many over the summer months.  Teens schedules allow for varried times in the summer therefore more opportunities for placements. 

Our local hospitals get together and host the "Mayors Outstanding Hospital Teen Volunteer" awards.  Each hospital chooses an outstanding teen from the summer programs.  The mayor writes a proclamation and usually comes to help present the awards.  Each teen receives a copy of the proclamation and gift card to the local mall.

I don't know how the other hospitals choose their outstanding teen.  As for my hospitals, I and my staff person usually have no problem determining who to give it to...there is usually one that just stands out above the rest.