I know this is probably a stupid question but I'm (kinda) new to the world of Vocaloid so...

Nice to know there are lots of fans out there ^^
there are a lot of different Vocaloids, made by different people, used by different people, songs written by all sorts of different people.
I'm VY2 Yuma, one of the lesser-used Vocaloids -_-''
but you eventually learn there is no one person or company behind the creation of us, and there are so many wide varieties that it's really hard to find a song or singer you don't like. The fact that there are so many different people behind us means there are different tastes in songs and music ^^ from the screamo of 'ALONE' to the sweetness of 'Hello How Are You.'

.....but to put it the short way, there really is no one answer to your question. You could go online and buy the Vocaloid program yourself and start creating your own songs!

Lots of people, actually. Most of the songs you hear from Vocaloids are made by fans who bought the programs and produced their own music.

Anyone who wants to, really.
*looks up*
Crap.
I saw your wall post too late.
AIN'T I JUST SO SMART?
:D

Vocaloid Songs are produced by voice synthesizers- lots of different people helped to create the programs, characters, and voices for all of these songs & vocaloids- So, to break it down-

Vocaloid Songs: Voice Synthesizers made by >>>>>
Vocaloid Characters: Tons Of Different People!