Popular songs from musicals:
When I grow up (Matilda)
Do you hear the people sing? (Les Mis)
Defying Gravity (Wicked)
Do ray me (Sound of Music)
Pure Imagination (Charlie and the Chocolate Factory)
Flash Bang Wallop (Half a sixpence)
Be kind to your Parents (Fanny?)
It's a hard knock life (Annie)
Consider yourself (Oliver)
Any Dream will do (Joseph)
We're Six (Six the musical)
Bipperdy Bopperty Bo (Cinderella)
Supercalifragilisticexpialidocious (Mary Poppins)
We're all in it together (High School Musical)
Grease Lighting (Grease)
Working 9 to 5 (musical by same name)
Are all ones that work well with groups and are easy to sing. Some of them have small amount of harmony/group work. These are all ones I've done with small chorus groups on stage.
There are ones that can be fun to do, but are harder to do.
"Pick out a simple tune" from Half a Sixpence, is fun, but unless they really are confident (you need a few to be able to do solo lines) it will sound flat.
Or "If I had money to burn" again from Half a Sixpence, is fun but more complicated.
If you're going for anything in concert be aware that Disney can be a pain about licencing anything and can be vicious in going for anyone using their tunes, yes even small charity events.
If you're wanting popular musicals for teens, I'd go for Six, Heathers, Les Mis, Wicked and if you look through the songs then you may find that some of them catch your eye.
Another thing you can do is ask them all to find one musical song they really like and put it in a box and choose some of them, I've done that and sometimes you get surprised by what they want.
If you want a bit of fun, you can rewrite some to be more relevant. Both favourite Things and So Long, Farewell (from Sound of Music) lend themselves well to that - some of them might even enjoy doing it.
On the whole I find upbeat ones they enjoy more, but quieter ones can be easier for them to learn. It's also worth giving them You-tube links so they can listen to them at home, because the more confident any one of them is, the more confident the whole group becomes.