I'd probably draw a path on a solid for the arrow to follow. Set a keyframe on mask shape.
Create your arrow point on a separate layer. Copy the mask keyframe and paste into the position parameter of the arrow point layer. For this layer enable 'autorotate along motion path' in the Layer Transform settings.
Apply the 'stroke' effect to the solid and animate the start-and endpoint of the stroke.
And then tweak to get the wanted timing and effect.
Barend's technique is a good one to use however if you use the "Write On" effect instead of the Stroke effect you can link the Brush Position parameter to the Shape layer's position parameter with an expression so that the end of the path always follows the shape layer. This way the two will always match, even if retimed.
You can also make sure that the arrowhead automatically orients to the path by selecting it and going to Layer > Transform > Auto Orient. And choose Orient along Path.
Hope this helps.
Angie Taylor animation & illustration for television, film, web and devices
In addition to the good suggestions from Angie and Barend, you could create your straight arrow in a precomp and apply Bezier Warp (or Mesh Warp or the Puppet Tool) to the precomp to animate the whole thing.
- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')
No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.
I know this post is very old, but I wanted to share in case it helps other people searching like I have.
We've developed this new After Effects script, Easy Arrows, which allows you to attach an auto-orienting arrow (or any shape) to a stroke, with the click of a button. https://modio.tv/downloads/easy-arrows/