I'm thin with a chubby face. When I smile I get a roll under my chin. Treatment options? (Photos)

easy and to the point solution is a simple tumescent fine liposculpture of that area.  It takes 15 minutes under mild sedation local.  Thanks for great question 

You are young with excellent skin quality and mild submental lipodystrophy.  I would suggest Kybella which is a simple and permanent solution.

A full set of facial photos at rest and smiling  along with an in-person examination is required to make a determination about which surgical procedure would be the most helpful.  Liposuction can accomplish removal of fatty deposits in the neck.  In our practice, we do not remove any fatty pockets in the face since your face will lose  facial fat with aging process  over time anyway.

The majority of slim young people perform a double chin have some imbalance in the between the mandible and maxilla(jaw and midface)
In your case I believe you have a strong masculine face that's well-balanced and you shouldn't be less concerned about the minor fold shown while you're smiling.
Others perception of you smiling will be focused on your mouth and eyes and not on your chin or neck.
For those who have a mandible that's insufficient chin implants may be a viable option.
Your mandible maybe just slightly small in relationship to your maxilla but you also have a pointed chin.
Adding a small chin implant  with possible chin liposuction could create a better facial balance but my clinical instinct is to except your face for who you are knowing that at least in my opinion you have a strong masculine face that does not need intervention.And in person consultation could give a more accurate assessment and you will probably find many different opinions to your concern.
Best,
Mats Hagstrom, MD

 Hi, I have performed many facial shaping procedures, including Chin Augmentation with dermal fillers or silastic chin implants, for over 30 years.  From the photos, your chin is quite weak.  When the chin is weak, this creates an imbalance making the nose appear larger, the mid face top heavy, the lower face looks short, de-emphasizes the lips and allows early formation of a "double chin".  
 Proper placement of a silastic chin implant adds forward projection to the chin thereby creating harmony and balance to the lower face.  Using the same incision, liposuction can be performed to reduce the fat and further shape the neck.  Excess skin, from below the chin, can also be removed through the same incision.  
 I have found that placement of a silastic chin implant, through a small curved incision under the chin (also allows excess skin removal) to be very safe, quick, highly effective and far less invasive than a sliding genioplasty (requires extensive tissue dissection, bone cuts and placement of metal screws and plates to secure the cut segments of bone).  I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone.  In my opinion, you are a good candidate for chin implant surgery.  
Hope this helps.