The DU Lounge

The ideal is ethyl acetate, or a glycol ether, but not everyone has bottles of that around the house. (Yes, I do.)
Even a high alcohol liquor will work.
If it's been there a while, it will take some elbow grease.
The 70% isopropanol found at any drug store should work.
Also toluene, available at most hardware stores will work, but do it in a WELL ventilated area.
Finally, be careful with acetone. Not all plastics play well with acetone. It can damage the surface of your whiteboard, depending on what it's made out of. For instance, polystyrene will dissolve almost instantly in acetone. Now, there's zero chance your whiteboard is made out of polystyrene, but you get the idea.