You don't. After you give him the balloon, he just floats away. He is seen again during the Scooter Chase, and on the televisions in the TV Store on Reality TV Island.
The country side
Green.
Being smaller than the other Poptropicans, he is lifted up by the balloon and floats away. We do not see him again except during the Scooter Chase. The reason for his fate is to distract the guy in the Web Browser cafe so that you can talk to im about his Underground tickets.
The kid who wants a balloon (specifically a greenone, virt) is in the Countryside with his mom.
The game doesn't tell you. He can be seen on the newscasts on Reality TV island. He may make an appearance on a future island.
From the store with the two mimes in front of it. PICK A GREEN ONE!
You don't need to. (He is still floating in the scooter chase scene, and the news is still showing his story on Reality TV Island.)
There's nothing you can really do but continue your mission to find out who took the painting.
Strangely enough, no. You can still see him floating during the later "scooter chase" scene.
Bob
You don't. It gets the attention of the guy playing the computer game and if you return his tickets he gives you one.