You draw mask around it and then use a Stroke effect that uses the mask as a path. Then you animate the Start/ End parameters. Similarly, you could use a shape layer with a path, a Stroke and a Trim Paths modifier.
A png file can be an image of anything. I don't know what a neon line trace is. I'm assuming that you have some kind of an image and you want to trace around the image with an outline that looks like a neon tube light at night.
The trace can be accomplished with a mask path that has stroke applied. You can apply other filters to the stroke like Glow to make give it the glowing effect. I'd start with a black solid, place it above your image, set the blend mode to screen, then use the pen tool to draw your outline. Then add stroke, pick a color, animate the start or end point to animate the line, then experiment with adding glow or duplicating the layer and adding some blurs until you come up with the look you're after.
It's the same technique that would be used to create a light saber effect except you're using a stroke instead of a solid.