Hemifacial Spasm: This condition is characterized by involuntary twitching or spasms of the facial muscles, typically on one side of the face. It can be caused by irritation of the facial nerve and is more common in women.

Blepharospasm: A condition that affects the muscles around the eyes, causing involuntary twitching or spasms. It can be a standalone condition or part of a broader syndrome.
Facial Tics: Part of a tic disorder, such as Tourette syndrome, where individuals experience sudden, repetitive movements or sounds. Facial tics can manifest as twitching.
Anxiety or Stress-related Twitching: High levels of anxiety or stress can cause facial twitching due to muscle tension.

Multiple Sclerosis: A chronic autoimmune disease that can cause a wide range of neurological symptoms, including facial twitching due to demyelination of nerve fibers.
Stroke or Transient Ischemic Attack (TIA): Although rare in a 16-year-old, a stroke or TIA can cause sudden onset of facial weakness or twitching and is a medical emergency.
Neurodegenerative Disorders: Such as Huntington's disease, which can present with movement disorders, including facial twitching, although it's rare to present at this age.

Dystonia: A movement disorder that can cause involuntary muscle contractions, leading to repetitive movements or abnormal postures. Facial dystonia can cause twitching.
Myokymia: A condition characterized by spontaneous, wave-like contractions of muscle fibers, which can cause facial twitching.
Neuromyotonia: A rare condition that affects the nerve-muscle interface, leading to muscle stiffness, cramps, and twitching, which can include the face.