This is the simple one; magic missile has no attack roll or saving throw, so nothing can stop it short of something that specifically calls out that it is capable of doing so (such as the Shield spell, for example).
Note how it just says:
Each dart hits a creature of your choice that you can see within range.
Mage Hand does not specifically have any interaction with any attack spells, but there is a simple option available to everyone that lets you “block” Firebolt, which would be taking the Dodge action.
If you tell me “I’m taking the Dodge action and I’m going to try and block any incoming attacks with my Mage Hand” then sure, I’d let you do that. Of course, you could also take that action with an active Mage Hand and the result would be the same, but it’s cooler this way.
The basic reason why the question has no real answer other than the above is that you ask “If you place it in the way of the spell”, but the Mage Hand does not give any of its own mechanics for doing that, so mechanically you can’t do it. At best, you can use some other mechanic to do roughly the same.
Note that if you want a giant hand that blocks attacks and enemies coming for you, you want Bigby’s Hand, but that’s a 5th level spell, not a cantrip, and it gives you an idea of how powerful something like that is.