I really hate the crease under my butt. It is completely devoid of fat. What can I do help its appearance? (photo)

Unfortunately this is a common problem after liposuction of this area. Although the result may not be perfect, there is usually some improvement with strategic fat grafting back into this area. If the fat grafting fails to produce a satisfactory outcome then a lower buttock tuck maybe your final option. Glad to be of help.

an in person consultation  would be extremely beneficial for you and the surgeon. Its impossible to tell based on the photo you submitted.  The skin at the bottom of the buttock can be trimmed to give your buttock a tighter appearance.   Please be sure to choose a Board Certified Plastic Surgeon who specializes in this procedure and is well known for it. 

Hello dear!
Thanks for the question and provided information as well.
Based on your pictures, you are a good candidate for liposuction with fat transfer, to improve your buttocks, and I think you'll get very good results. 
In general, you need to be physically healthy and at a stable weight, have realistic expectations, be a non-smoker and your BMI needs to be 30 or less.
l recommend you to make an appointment with a board certified plastic surgeon to talk about your goals and anything you need to know.
Good luck :)

 When fat is removed from the posterior thigh, the buttock  becomes destabilized. There is no support to push it up and there is no smooth contour between the Buttock and the thigh. The solution to this problem is Liposuction Of fat from somewhere in your body where you have excess fat and placing that fat in the buttock/thigh interface to smooth it out. This is a common deformity seen when Surgeons liposuction the posterior thigh. If you look at my Instagram page I always graft fat into the posterior thigh to support the Buttock. I have attached a link for your review. Best regards