There aren't many cantrips that I know of which inflict a status effect, so I wanted to create one. The aim is to make it strong enough that it's viable, but not so strong that it's a must pick.
Here is the cantrip in question. I haven't settled on a name, so I've put both.
Illusion cantrip (Sorcerer, Warlock)
Casting Time: 1 action
Range: 60 feet
Components: S, M (sleep dust)
Duration: 1 round
You briefly implant terrifying visions into a creature's mind. A construct or undead is immune to this effect. The target must succeed on a Wisdom saving throw or become frightened of you until the beginning of your next turn.
The number of creatures you can target with this spell increases by one at 5th (2 creatures), 11th (3 creatures), and 17th level (4 creatures).
Cause fear is a first level spell that targets one creature, and lasts a minute with concentration, allowing a save at the end of the creature's turns. In comparison, this cantrip also only targets one creature, and only lasts a round.