Child prostitution rackets operate in almost 1,000 municipalities in Brazil, according to a government study mapping the underground industry.
In Brazil's cities, thousands sell sex to Western tourists
Almost one in five of the country's large cities harbours well-organised under-age sex rings, officials say.
Activity is especially rife along the triple border where Brazil, Paraguay and Argentina meet.
The study was published by Brazil's Human Rights Secretariat and the UN children's organisation, Unicef.
"By 2006, we want to reduce by half the number of municipalities involved in this, and reduce the number of children and adolescents who are victims of exploitation," said Brazil's Human Rights Secretary, Nilmario Miranda.
The government says it cannot put a figure on the number of children and adolescents involved in the industry.
Mr Miranda added that, until recently, the issue was not taken seriously by authorities.
The country's megacities of Rio de Janeiro and Sao Paulo are home to about a quarter of the total number of child prostitution rings, Mr Miranda said.
And nearly a third of all rackets are located in the impoverished north-east of the country.
Brazil's poverty - nearly 15% of the population live under on under a dollar a day and its relatively youthful population - some 40% of people are under the age of 18 - contribute to making it a hub for sex tourism.
Mr Miranda said Brazil was working with authorities in Germany, Italy and the Netherlands - the principal source of sex tourists - to fight the problem.