I wonder how we can put sympathetic magic in a 5e D&D class.
For my homebrew witch class, I have a series of specific supernatural powers (akin to Pathfinder's "hexes" for their Witch class) that I call "Crafts." [Geddit? "Witch's Crafts?" I crack me up.] Among them, what probably most fits your desire, is called "Poppet."
As you might expect, it's a poppet. And, yes, you need some piece/thing of the target creature (hair, fingernail, a scrap of clothing, or personal possession, etc...) to use the poppet on the target. It requires an hour of making/enchanting (using the craft). The target must be observed for a minimum of (an additional) one hour. The poppet will only function for the witch that creates it.
Once complete, while the poppet is in the witch's possession, and the target is in the witch's presence, the target will act/react as if under a Charm Person spell. No save. At 3rd level, the witch can whisper direction to the poppet up to 10 x level feet away and the target will comply. At 5th level, the witch can use the poppet to instill a Suggestion spell on the target, once per day.
The poppet lasts one day per witch level, unless the poppet's "trigger" (if you will) is a physical piece of the target: hair, fingernail, a few drops of blood,...a finger, etc... in which case the connection is indefinite until the poppet is destroyed (or witch that made it dies). A witch can never have more poppets enchanted than their Cha or Int modifier (whichever is higher).
Really, if a player wanted, they could fluff many of the witch's supernatural (non-spell) powers as, essentially or implicitly "sympathetic magic." The PC always pulls out a nondescript poppet, or a specific crystal (any "arcane focus," basically), rubs their family heirloom jeweled pendant, or the arranges bones on the ground in different patterns to use any craft/cast any spell. But I understand you're looking for a specific mechanical thing.
That's not especially satisfying, IMO. I'd like to find a way to specifically do sympathetic magic, or provide some manner of benefit for creating sympathetic links between components and subject.
Using the above as a base mechanic, you could tweak it to include/apply to targets of any of the Witch's powers/spells...as a ritual performed at a distance...require a physical object/piece of the target (a side quest/part of the adventure all its own) to a certain distance that increases with level.
A low level witch could "hex" you from around a corner, for example. The local Coven Queen might be miles away.