Can you cast Mage Armor on more than one creature at a time? I haven't found anything that says either way.
The spell Mage Armor specifies that
you touch a willing creature
Spells do what they say, so Mage Armor works on a willing creature, with the singular article -- only one target.
That said, Mage Armor seems eligible for the Sorcerer metamagic Twinned Spell, which could cause it to target two creatures.
There is also no reason you cannot cast Mage Armor more than once on different targets, assuming you have the available spell slots, since it is not concentration. You cannot have multiple copies of Mage Armor affecting a single creature, however -- or, rather, only one will have any effect.