I started a game, which is called Cuboid Ninjas, but I am horrible at art. The art dimensions would range in sizes from 16x16 to 800x600. They would not be getting paid, but they would get half of the donations (I wouldn’t pay them regularly, they only get half of donations). I only need 1 person, so I need to see some past work and a way to contact you (skype would be best!)
The game concept so far:
After rival ninja groups and samurai groups team up and steal your book of ninja magic, you have to battle members of the large rival group, known as 'the Dark Ones'. As you defeat the Dark Ones' members, you collect mana and loose pages of your ninja spell book along the way. With the mana that you collect, you can upgrade the levels of your spells and also upgrade your weapons, making you stronger. But as you get stronger, the enemies also slowly get stronger, and begin getting harder to defeat. But as you go, the days that it is taking you to get all your pages is raising. You learn your Sensei has been cursed, and his days are numbered. You also learn that the only way for him to get better is if you get back your full spell book and cast a large spell. But once time runs out, it is game over for you, and you will be forced to restart unless you have a special item you can get along the way.
Oh yeah, it will be a sidescroller, so that’s the kind of art I will need. (I will also need characters, a logo, icons, buttons, landscape, etc.)
Where can we play the demo? 
Unless you are planning on being the artist, you can not play it yet 
[quote]They would not be getting paid, but they would get half of the donations (I wouldn’t pay them regularly, they only get half of donations)
[/quote]
You realize you repeated yourself, yeah?
If you want an artist, first off, you’ll need to show something to at least prove that you are capable of doing something with their art. Second, “sidescroller” isn’t a type of art.
I’d also like to see some progress.
If your game will be canceled, all the work is useless.
You won’t find many artist doing free work, especially if there’s a lot of it. Check out http://www.pixeljoint.com/forum/. Haven’t had issues with it personally but I’ve seen posts claiming that either the artist or costumer have been ripped off - but they get blacklisted.
A better way is to have a working game with placeholder art, then get the artist to make the real art.
Also, before asking people to show previous work so they can work with you, it might be a good idea to do the the same.