Is being naturally too skinny a turnoff?

Turn off? No way. Ribs are hot. be proud of your skinny body. All the girls would die to have your body.

No, its fine. I only found your question cause I was looking for skinny girls on the net cause they turn me on so much. Just find someone who loves what you are. Simple
Stew.

I am the same way, I work out, drink protein shakes, etc and am still really thin for a guy my height, but as far girls go, as long as she has a healthy weight, meaning she isn't a giant skeleton with skin, so if doctors say it's ok, then I see no problem with it.

Whatever your body type is, be happy with it. It matters not how fat or thin you are, as people can be attractive both ways, either too wide, or too thin. For many men the "ideal" body, would not be TOO thin, but thinner than average. It doesn't mean that you are necessarily ugly.
I particularly like thin girls. You don't need a large chest, beefy legs, or plump ass, what a girl needs for me, is a good form. I love the physical beauty of all slender girls. It is just who I am. I think that If you are Healthy, and skinny, then you are almost automatically attractive.
It is my opinion, but I know that I am not alone with this.

Be happy, Be healthy, and you will be more attractive than anyone else, regardless of your body type.

I know skinny girls who get a lot of attention from guys so it's definitely not a turnoff. There are a lot of guys who would find that attractive, you just should be more confident.