We don't recommend detoxes or fasting, whether it's juice or something else. It is better to eat balanced meals. Here's an Ask the Expert page that addresses this: www.sparkpeople.com/community/ask_the_expe
I'm not sure what you have tried before, but I would recommend tracking your food and your fitness activities. Tracking your food and seeing what your intake is will be a great factor in your weight loss. If you have been tracking your food, are you within your ranges for calories and nutrients?