US politicians have called for federal action to prevent parents from giving unwanted adopted children to strangers met on the Internet.
The Illinois attorney general has urged Facebook and Yahoo to police online groups where children may be advertised.
The demands come as nations whose orphans have been adopted by Americans contend that the US government is not doing enough to stop the practice, known as "private re-homing."
An investigation by Reuters last month revealed an underground market where desperate parents seek new families for children they adopted but no longer want.
The parents connect through online forums on Yahoo and Facebook, privately arranging custody transfers that can bypass government oversight and sometimes violate the law.
No government agencies track the practice, but the news service identified eight Internet groups in which members discussed, facilitated or engaged in re-homing.
In a single Yahoo group that the company has since taken down, a child was offered to strangers on average once a week during a five-year period.
At least 70% of those children were listed as having been adopted from overseas.
The series identified re-homed children who endured severe abuse and adults who used the online network to obtain children but were not properly vetted.
In one case, a man now serving prison time for child pornography took home a 10-year-old boy he and a friend found online earlier that day.
They picked up the boy in a motel car park.
18 federal politicians called for a Congressional hearing on re-homing.
In a letter submitted to a House subcommittee that oversees adoption, the bipartisan group said the news agency's series "drew attention to the many disturbing dangers and problems associated with this practice."
In the letter, the US politicians also requested a study by the investigative arm of Congress, the Government Accountability Office.
The study would identify gaps in state and federal laws "related to the oversight and prosecution of wrong-doers in the re-homing of children."
It also would identify ways to better support struggling adoptive families.
In a letter to Obama administration officials, it called for a broad federal response.
The Reuters stories demonstrated that advertising children online "does not seem to violate any federal laws"
An agreement among states is supposed to prohibit parents from transferring custody of a child to a non-relative across state lines without approval of officials in both states.
But the agreement is rarely enforced.
Some state laws prohibit anyone without a child-placing license from facilitating adoptions or advertising children for adoption.
Many states place no restrictions on the activity, and no uniform federal law exists.
The apparent lack of response by US authorities to re-homing has angered some nations.
Days after the articles were published, the Democratic Republic of Congo announced it was not allowing children to leave the country for adoption.
"This suspension is due to concerns over reports that children may be either abused by adoptive families or adopted by a second set of parents once in their receiving countries," according to a US State Department alert posted 27 September on its website.
Congolese officials did not comment.
China and Russia are among other countries that expressed concern over the US government's handling of the issue.
