It is a little unusual for a 27 year old to have loose skin on their face following weight loss of even a significant degree. Usually at that age the skin has enough elasticity to accommodate the loss of volume. In general however, loss of weight produces a loss of overall subcutaneous volume in the face. This can lead to the loss of skin tone or facial structural shape in a young person, and an aging appearance in an older person. Loss of volume in the cheek and area around the eyes can be replaced by performing a fat transfer. This involves harvesting remaining fat from the body or lower limbs and placing it into the appropriate areas of the face to add contour. This can include augmenting the cheeks or jaw area. Sagging neck skin usually is dealt with by performing a surgical procedure to tighten the skin. There is some anecdotal discussion about lasers producing skin tightening, but I have never been impressed with this in the neck. In someone of your age usually a tightening of the neck musculature called a platysmaplasty will be sufficient.
The best way for me to address your specific concerns is to come in for a consultation. There we would be able to discuss the procedures in more detail and be certain to meet your goals.