There is no way to lengthen the neck safely. However, there are various ways to make the neck appear thinner and longer, such as proper clothing, exercise, posture and surgery.
Make the neck look longer by wearing v-neck or scoop-neck shirts, which elongate its appearance. Try adding a lightweight necklace that falls around the collarbone, drawing the eye to the base of the neck.
Practicing good posture naturally elongates the look of the neck. Poor posture creates a shorter-looking neckline. Putting the hair up or wearing it in a short style also makes the neck appear longer. Exercises that work the muscles of the chin, jaw, neck and shoulders tone these muscles to create a slimmer look. Liposuction is able to remove fat around the neck to make it thinner, but no surgery actually elongates the neck. This surgery is an extreme measure.
Some cultures place considerable importance on a long neck and use neck rings to extend it. Copper or gold rings are welded together around the neck, stretching it over time. These rings are fairly permanent and are worn continuously. It is a dangerous practice; taking off the rings after an extended period sometimes causes serious damage and injures nerves in the neck. The reliance of the neck on the support of the rings often means that the neck is no longer be able to support the head without them.