Sculptra for Loose Neck Skin?

It is very difficult to make a recommendation without seeing you in person.  However, it sounds like from what you are describing, you may be a better candidate for surgery to address the loose skin under your neck. 

Thank
you for your question. It is quite difficult to give you advice without seeing
a photo or examining you in person. Generally loose skin in the neck and jowls
require surgery. Sculptra can only be used to increase volume to some extent. I
recommend consulting an expert to evaluate your concerns for the beat treatment
plan. Best of luck!

Liposuction is useful to reduce fatty deposits. Many surgeons are now using ultrasound or laser with the liposuction to add energy and heat which seems to help tighten the skin and reduce post operative swelling and bruising.
In general, fillers are used to add volume. Sometimes, volume can be added to the cheeks and around the eye to lift the skin below. Often Sculptra or Juvederm Ultra Plus works well for these types of volumizing procedures. You may also consider tightening the skin with a resurfacing laser such as a Sciton or Affirm or similar laser that tightens the skin. Certainly facelifts will help reduce unwanted loose skin as well. Most often a combination of treatments works best.