The View Orders page in Back Office (Back Office -> Orders -> View Orders) now has a new Order Number field that you can use to search for a specific order number, as shown in the screen shot below:
You can enter just the numeric part of the order number (e.g. "12345") or the whole thing (e.g. "ORD-2012-12345"). Just remember to leave all of the other search fields as blank or "All" (in the case of the drop-down boxes) so that you are just searching for the order number by itself.
For example, if you enter an order number but leave the Order Status drop-down box as the default value of "Created", then unless the order number you entered has a status of "Created", no orders will be returned.