Your Manga character's face is nearly complete. Now you need to shade the hair. In general, Manga artists pick a section of the hair to be highlighted and shade accordingly. Hair is typically shiny, and therefore shaded with high contrast. In other words, the change from dark to light happens abruptly over a short distance rather than gradually over longer distance. Use a photographic reference if you have any doubt about how your highlights should look.
Lastly, draw lines down from the chin curved slightly inward. These simple lines make up your character’s neck. In general, men have thicker necks than women, but keep in mind that the age of the character matters as well. In Manga, very old and very young males are usually drawn with skinny necks. You are can shade the neck and face if you wish, but keep it simple and don’t over do it.
And your Manga character is finished!