But police officials and advocates say that whatever the number of victims, it is growing. Thousands of women are forced to work — often for even lower pay now, because of the economic downturn — everywhere from fancy clubs and private apartments to industrial complexes and lonely country roads.

Europe woke up to the problem of trafficked women in the 1990s, as young women from the former Soviet Union began to arrive in large numbers, and it has spent much of the last decade developing legal frameworks to address the issue. But, some advocates say, this decade will test Europe’s commitment to enforcing its new laws.

“The structures, by and large, are in place,” said Luis CdeBaca, the ambassador who leads the State Department’s Office to Monitor and Combat Trafficking in Persons. “Now it’s time to take them out for a drive.”

Fueling the boom in the sex industry in Spain are many factors, experts say, including porous borders in many parts of the world and lax laws. Until 2010, Spain did not even have a law that distinguished trafficking from illegal immigration. And advocates say arrests of traffickers and services for trafficked women remain few. The State Department’s report on trafficking said that according to preliminary information, the Spanish government prosecuted 202 trafficking suspects and convicted 80 in 2010.

More important, some advocates say, is the growing demand for sex services from younger tourists. Of course, there is a local market. One study cited by a 2009 United Nations report said that 39 percent of Spanish men admitted having visited a prostitute at least once. It is widely accepted here for business meetings to end in dinner and a visit to a brothel.

But more recently, experts say, Spain has also become a go-to destination for sex services.

In La Jonquera, tucked behind an all-night gas station, is the newly opened Club Paradise, which, with 101 rooms, is one of the largest brothels in Europe. It caters in large part to young men from France, where many aspects of prostitution are illegal, and perhaps more to the point, buying sex is more expensive.