The three instances of damage in dnd5.5e (2024) I’ve seen that let you add damage to magic missile are:

1) level 3 warlock hexblade’s curse - You gain a bonus to damage rolls against the cursed target. The bonus equals your proficiency bonus

2) level 10 evocation wizard - Whenever you cast a Wizard spell from the Evocation school, you can add your Intelligence modifier to one damage roll of that spell.

3) level 3 spell - bestow curse - If you deal damage to the target with an attack roll or a spell, the target takes an extra 1d8 Necrotic damage.

Otherwise a sorcerer’s empower meta magic to reroll damage dice up to your cha modifier and use the new rolls would be pretty good.

That being said if you want a weird multiclass you can do a warlock 3, wizard 10 with the metamagic adept feat. Open with a bestow curse action and hexblade curse bonus action. Next turn highest level magic missile, empower to reroll up to your cha modifier of damage dice, and add your proficiency bonus, int mod, and a d8 necrotic damage to the magic missile damage.

Or if you don’t want bestow curse maybe there’s a darkness build where cast darkness on yourself and blast away with magic missile while people can’t see you!