According to Statistic Brain, as of 2014, total spending by American youths aged 13 to 19 years is approximately $258.7 billion annually. According to Business Insider, teens spend 40 percent of their money on clothing. If that's correct, it translates to $103.48 billion spent by teens annually for clothes.
It is difficult to tell how accurate these numbers are. Statistic Brain claims that there are 26,873,000 teenagers in America in 2014. That means that the average American teen is spending nearly $10,000 annually, with almost $4,000 spent on clothing. However, the U.S. Bureau of Labor and Statistics page on consumer expenditures notes that for 2012 to 2013, the average household spent $1,706 on apparel and services.