After effects: Moving text along 3D path
to accomplish this, we need to cheat something. I assume you are trying to do something like this in the following image:




First, create a camera in your comp (i see you already have one)
Then create a text layer and make it 3D (you have this as well)
Select your layer and select Ellipse tool (Q) but do not apply
anything.
While your text layer selected, double click the Ellipse tool in
your toolbar. This will create a circular mask on your text layer.
Rotate your Text layer -90 degrees on X Axis.
Twirl down the controls of the Text layer and under Text controls
you will see Path Options. In these options select your mask. And
change your settings as you wish.
Now expand all the controls of that layer. There you will see a text
label Animate: with a small circled arrow.
Select Enable Per-character 3D.
Then in the same menu, select Rotation.
There will be an Animator 1 section, expand it and change the X
 Rotation to 90 degrees.


Now check with your camera, orbit around, you should see your text bends through your mask.

To animate this text along that path, get back to the Path Options. Keyframe the First Margin option or add an expression by Alt+Left Click, and add this value and edit as you like:

time * 500


This will get the current frame and multiply it with 500 and give this value to First Margin property.

I am also adding the link for the project, but you need at least CS5.5 to open: http://www.mediafire.com/?13dl3x67w4v5yod