How to animate the outlines of text (After Effects)
Simplest way is to use the Stroke Effect on a solid layer with separate letters as masks.


Create a new solid
Write your text in Illustrator
Convert it to a path
Seperate all letters  with the path finder or ungroup it 
Setup same document size as in After Effects   
Import your paths into after effects, pasting should also work with CTRL+V. Requirement is to have all of your paths from Illustrator as seperate masks on the solid in After Effects.
Note: you can create seperate paths from an image of letters within After Effects with the auto trace option (Layer > Auto Trace) - use black and white option and set it to the current frame (Note: Tracing letters isn't really accurate)
Apply the stroke effect to the solid layer which should be full of masks now
Tick All Masks option to make use of all masks
Set the paint style to transparent
Go to your first frame and set the End value of the effect to 0%
Click the stop watch of it to enable animation
Go to your last frame and set the End value to 100%


You can play with the settings of the effect, but in general this should do what you want to achieve. 

Note: The order of masks determines the order of the animation. To reverse the effect simply duplicate the first keyframe and move it behind the second one.