I’ve done something similar with a picture i wanted it to fly in and fill in the picture from left to right. ayatoweb.com has a very nice walk through kinda guide how to do it. not a full tutorial but its easy to pull off. basically it using the shatter effect but reversing it so that it fills in you can pretty much get the shap of your “particles” to be anything you want. look into it it might do the job your looking for to simulate particles filling in an object or logo.
Jake