Weddingbee boards

I would try going the custom route for your situation. Because you are so petite even altering a pre-designed dress wouldn't look right on your frame, the proportions would be all off! I would find pictures of a styles you like and take them to a talented dress maker so they can fit your body/proportions correctly.

In terms of what to look for I would stay away from ball gown and drop waist styles. A ball gown will give you that "flower girl" look because you are so small (I know the feeling, I'm only 5'0 100 pounds). A fit and flare or modified a-aline silhouette would look nice. If you have no butt I would stay away from mermaid and trumpet dresses as they need curves to help fill them out. I would also look for a sweetheart neckline as it will give you a little more up top. 

This would look gorgeous:

A style like this would look great on you too as it would define your waist: 

@Totes Magotes: It is a Jim Hjelm dress. Like I said, though, I would maybe try on a few dresses and then go the complete custom route. Altering a dress that was meant to fit someone a foot taller and 50 pounds heavier than you (even if you can order hollow to hem) won't look right because the proportions would still look off.