Hey there

May I ask...are you asking this because you want to know for personal reasons or are you writing a research paper of some sort? 

There are many articles here on Health Central to get you started on your search for information.  Here is but one article of many.

I can also tell you personally that teen depression not only affects the person who is depressed but like you are asking...the family, friends, and classmates.

I had a friend in high school who suffered from both depression and an eating disorder.  My friend's problems soon became noticeable with great weight loss and her family was alarmed.  Her family became more and more controlling to try to combat her seemingly out of control symptoms and in turn this caused her to be more angry and depressed.  I was both her classmate and her friend and she did turn to me at one point for help.  Other friends became afraid that they too could experience this disorder.  One of our teachers pulled me aside one day and told me that I had to do something.  I felt a lot of pressure and helplessness of what to do. Family, friends and I also felt a little guilty because when a loved one or friend is depressed you feel like maybe you are in some way responsible.  Finally her family and I convinced her to see a therapist and I went with her to her first appointment. 

So there is but one example for you.