shipment has been lost vs ~is missing
Solution 1:
Actually, it would be more natural to say "A shipment worth a million dollars...".
As to "is missing" vs "has been lost", the former implies that the shipment can't be located but may simply be in transit or whatever and might show up on its own.
Since "lost" has two somewhat different meanings in this sort of context, "has been lost" implies either that the disappearance is permanent or that the "loss" was the result of carelessness (or both).