You have to use public URLs to the file. There can't be a Google Drive/Dropbox account support, because the API GMod provides can't.

Dropbox has a public folder. So you can move things there. Im not sure about Google Drive, though.

With google drive I think you can make it so that the sharing option says it is public. If that is what you mean.

The important thing is that you have to have an URL that hot links to the file that would works for everyone who would click it.

I have tried that already and it said File is unsupported. :(

When you enter that link in the browser, does it direct you to a page with a download button or "please wait" on it or does it start the file download immediately?

When the URL leads to the said webpage, than the radio will have the error "file is unsupported", because it tries to play a HTML file.

It goes straight to the file, however it doesn't seem to play automaticly:
https://drive.google.com/file/d/0B4kZYJzDAur2RUYyR0hYR1dIWk0/view
For an example

This leads to a webpage with a player or something on it which is not(!) the file itself. I don't think it wont let you hot link with a static URL to the file, so you can't play it with the radio via Google Drive. You should try Dropbox instead then.

Alright i've got it working with dropbox. Thanks

Because someone was asking: Drobbox has removed the public folder. However you can mark single files as puplic instead. You get a puplic URL you can use for playback if it doesn't lead to a splash/download page.