Not like you think.
You need to start with all the particles ON the shape, then be expelled into the surrounding space. You'll be turning that animation backward.
Start with an Emitter; Shape: Image (if something "custom" or different than the available options); Arrangement Random Fill (available for most options); Birth Rate 0; Initial Number -- whatever you need; Speed 0.
Add: Behavior > Simulations > Repel From
Add: Behovior > Simulations > Random Motion
Add another object that can be used to force the particles in the direction you want them to "come from" .
control the length of the animation by the setting the length of the behavior.
Clone the Emitter once you have the "reverse animation" to your liking.
With the Clone selected, go to Inspector > Properties > Timing and check the Reverse parameter. [Duplicate the emitter with no behaviors for a "hold" condition at the end.]
With the clone in reverse, your particles will appear to "stick" to a destination.
A little hard to explain well, but HTH.