These slides attempt to estimate the extent of the problem, and point out that teenage alcohol use is probably half of what it was in 1975. It has been declining for twenty years, due in part to raising the drinking age and public education campaigns against drunk driving.
Some studies tend to overestimate this problem, which is actually a declining one.
One fairly recent estimate places the number of heavy drinkers in age 12-to-21 group at 2 million and the number of alcoholics at about 1.1 million, but these estimates vary widely by age, social class, ethnicity, location and how the questions are framed.
Almost certainly there are far more ...