The use of the term "ghostwrite" in music has always confused me (on the very rare occasions when I've seen it used).
In the literary world, the term is used to describe someone who writes a book but does not receive credit ie: I'm writing my autobiography - but you're actually the one doing the writing - based on some general facts I provide (although your name never appears as the author/co-author)
In music, you would normally have a writer who's music is published and recorded by someone else - or perhaps someone who co-writes with an artist, but the artist records the song. In either case the writer recieved credit and is not a "ghostwriter"
Now, is it possible that an artist (let's use Madonna as an example) has claimed to write a song which was actually writen by someone else who remains uncredited? Maybe, although I don't recall ever hearing of such a case in any recent history. Normally, it seems if someone thinks their material is being used by someone, there is a lawsuit.
That being said are there "ghostwriters" in music - maybe. However, the term is not something normally associated with music.
I'm wondering if the question you intended to ask could be could be better phrased - is anyone looking for writers or co-writers?