"We just walk up and say 'vodka' or 'beer', because they may not speak Swedish. They bring it out, tell us the price and then we give them the money," one 15-year-old told Swedish Radio.
"I don't think it matters how old you are," he said.
Compared to five years ago, the number of bootlegging cases has doubled. Illegal sales are common in late spring, when Sweden's high school pupils attend graduation parties.
At 19, graduates are not yet old enough to buy alcohol from the state-run chain Systembolaget, which only accepts customers over 20.
Sweden's public health minister Maria Larsson of the Christian Democrat Party told Swedish Radio News that the government is constantly at work on the issue.
"We have allocated resources to combat this problem for the rest of the term. It's about working on attitudes, and about parents and children saying no to a greater extent. That's very meaningful," Maria Larsson said.