On Emperor, you can't rely on worker stealing alone. You will have to make at least 1 worker. You probably will never steal a worker from a civ, as by the time they have them, it will be hard to get past their defense. However, keep tabs on the near by city states. While it takes longer before they start to pump them out, they will start making workers and you can steal multiple workers from a single CS. Just don't make peace with them before it is done.
The trick with farming workers like this is to pick a spot that has an obstruction of view between the border and worked tile. They will not send a worker to a tile if they see you within 2 tiles, but if there is a hill, forest or jungle between the border and you, they will send the worker out to work the tile. You just have to occasionally use your scout to look over that obstacle. If they finish the tile improvement, you just need to pillage it so they will send the worker there.
I've taken 4 workers from a single CS this way on Emperor.