Neck/chin has lost shape after thyroid surgery what type of procedure would fix this?

This is difficult to answer without pictures. I find that VASER liposuction in combination with ThermiRF are best for contouring the chin in those who are candidates. If you have skin laxity, you may also be a candidate for a neck lift, which can be performed at the same time. Kybella can be used as an alternative with or without thermage/ultherapy/exilis or coolsculpting. I recommend getting a formal evaluation with an expert. Best, Dr. Emer.

Without photos, it's difficult to determine the treatment to address your concern. Also, it really depends on the amount of #sagging you are experiencing. It's best to begin by consulting with a surgeon in-person. The presence of banding down the front of the #neck, and, amount of excess skin and condition of your skin are among some factors which determine what treatments will best rejuvenate your neck . 
During your initial examination, your chin will be evaluated along with the neck and jawline. A weak #chin implies a lack of chin support for the skin along the neck line. In younger individuals a chin implant alone is usually all that is needed to improve the appearance of the neck. Subsequently, it will also improve the overall #balance of the face and can create the illusion of a smaller nose. As a stand-alone procedure, chin augmentation can be performed in the office under local #anesthesia. For individuals with signs of #aging in the neck, a chin implant added to one of the recommended procedures above, will provide optimal results.
Your board certified plastic surgeon should evaluate both your anatomical features and aesthetic goals to suggest which procedure best suits your needs. In some cases there may be more than one option to choose from. If you are not a candidate at the time of your #consultation, your board surgeon can recommend non-surgical alternatives to address your concern. 

Without an exam your question cannot be answered.  You will need to see an Oral/Maxillofacial surgeon to see if othognathic surgery, genioplasty or using an implant is best for your specific case. It should be noted that patients with severely weak jaws or abnormally functioning jaws may be better treated with other facial surgery (orthognathic surgery), although a chin augmentation may be an option at a later time. These patients should seek the advice of a plastic surgeon to determine which course is right for them. Here is some information to help you make this decision: Candidates for Chin Augmentation - Patients whose chin profiles are weak but have normally functioning jaws are candidates for Chin Augmentation. Many of these candidates have used injectable fillers in the past to strengthen the protrusion of their chins, but are looking for a permanent solution. If you are one of these patients, then you are a likely candidate for chin augmentation
#weakchin #chinimplant

Most likely a lower face-lift/neck lift type of procedure will work best for you. This procedure enables tightening of the neck muscles to eliminate bands and laxity under the skin, as well as a tightening/smoothing of the skin itself. A cleaner, lifted jawline with more of a "90 degree" angle for the neck profile is the result. The incisions used for this hide very well behind the ear.

Excess of skin in the neck ( as well of the neck muscle known as platysma) could be improved with a plastic surgery procedure called neck lift. This procedure, through small incisions behind the ear and behind the chin, tightens the neck muscle ( platysma) and redraws the neck skin behind the ears to give a rejuvenated look to the neck.Patients interested in neck rejuvenation  should make a consultation with a Board Certified Plastic Surgeon specialized in plastic surgery procedures of the face and neck 

Without photos, it is difficult to say, but if you don't have much fat, and it's mostly skin drooping, then a lifting procedure will definitely give you the longest lasting result. The key is to go to a facial plastic specialist who can evaluate you and give you the best advise.