Sudden Fat Loss Right Under Cheek Bones? (photo)

It looks like you could benefit from fillers at your age. This would add volume in your cheeks and other areas to give you a fuller appearance. You may also want to consider fat transfer.

When one notices greater hollow or experiences facial volume loss, we need to replenish volume somehow. While fat transfer or facial implant may be attractive given superior longevity, I personally believe temporary fillers such as Radiesse, Sculptra, or HA fillers such as Juvederm or Perlane should be performed first. Fat transfer often can result in uneven results after a period of time due to possible uneven rate of fat graft breakdown and it would be tricky to remove surgical implant if you are not thrilled with the clincal outcome. For most cases, I like to use Radiesse to provide instant gratification and consider Sculptra as a long-term project for maintenance. Perlane or Juvederm Ultra Plus is fine option as well if one needs a peace of mind for reversibility with hyaluronidase.

Posted photos demonstrate specific fat loss in sub malar and infra orbital zone. Cause hard to state over the internet without at least an in person examination. Treatment is fat grafting if you have donor fat areas. Seek expert in Fat Grafts. 

 Aesthetically speaking the cheek bones are quite small and flat and the buccal fat appears to have atrophied just below the cheeks making that area appear gaunt.  From the photo, I'd suggest cheek augmentation using a temporary filler (I perfer Perlane) or a permanent augmentation with Cheek Implants.  With the latter, I would decrease the fatty tissues in the nasolabial folds as they tend to block the anterior shape of the cheeks.  Be sure to select a plastic and cosmetic surgeon that understands and follows the proper aesthetics of facial beauty for the creation of naturally, more attractive cheeks and face.

Although I've seen this type of groove in patients as they age, I've not seen this in young men like yourself. Is there a family history of this cheek contour? I would fill this groove with injections of the patient's own fat or using fillers such as Radiesse or Restylane.

If there is no correctable underlying cause for this change, fat transfer or cheek implants should do well for you. There are other injectible fillers that might be recommended by others on this site. I am just more familiar with fat injections and silicone cheek implants.