Is it healthy for a 16 year old girl to go on a diet or do a juice detox?

Going on a diet often means restricting a person’s food intake and choices in order to lose weight. You may end up not getting enough of many important nutrients for good health.
The safest way for a teenager to lose weight is to increase physical activity so you burn more calories. Reducing intake of food and drinks high in fat and sugar, as well as watching portion sizes also help in weight control.
Juice detox (drinking only juices made from raw fruits and vegetables to cleanse the body from toxins) and other fad diets may cause you to lose weight quickly but the weight loss tend to be temporary. These diets lack major nutrients needed for overall health. Moreover, the weight usually comes back on when you return to your old eating habits and inactive lifestyle.
To learn more about healthy eating:
http://www.eatright.org
http://www.helpguide.org/articles/healthy-eating/healthy-eating.htm