The U.N. migration agency called on social media giants on Friday to make it harder for people smugglers to use their platforms to lure West African migrants to Libya where they can face detention, torture, slavery or death.
The smugglers often use Facebook to reach would-be migrants with false promises of jobs in Europe, International Organization for Migration spokesman Leonard Doyle said.
When migrants are tortured, video is also sometimes sent back to their families over WhatsApp, as a means of extortion, he said.
"We really ... ask social media companies to step up and behave in a responsible way when people are being lured to deaths, to their torture," Doyle told a Geneva news briefing.
There were no immediate replies from Facebook or WhatsApp to requests by Reuters for comment.
Hundreds of thousands of migrants have attempted to cross the Mediterranean to Europe since 2014 and 3,091 have died en route this year alone, many after passing through Libya.
This year, the number of migrants entering Europe is 165,000, about 100,000 fewer than all of last year, but the influx has presented a political problem for European countries.
IOM has been in discussions with social media providers about its concerns, Doyle said, adding: "And so far to very little effect. What they say is 'please tell us the pages and we will shut them down'.
"It is not our job to police Facebook's pages. Facebook should police its own pages," he said.
Africa represents a big and expanding market for social media but many people are unemployed and vulnerable, he said.
"Facebook is pushing out, seeking market share across West Africa and pushing out so-called free basics, which allows ... a 'dumb phone' to get access to Facebook. So you are one click from the smuggler, one click from the lies," he said.
Social media companies are "giving a turbo-charged communications channel to criminals, to smugglers, to traffickers, to exploiters", he added.
Images broadcast by CNN last month appeared to show migrants being auctioned off as slaves by Libyan traffickers. This sparked anger in Europe and Africa and highlighted the risks migrants face.
Doyle called for social media companies to invest in civic-minded media outreach and noted that on Google, pop-up windows appear if a user is looking at pornography images, to warn of danger or criminality.
The IOM has helped 13,000 migrants to return voluntarily to Nigeria, Guinea and other countries from Libya this year. It provides them with transport and pocket money and documents their often harrowing testimonies.
Doyle said it was currently repatriating 4,000 migrants to Niger. Switzerland said on Friday it was willing to take in up to 80 refugees in Libya in need of protection, among 5,000 whom the UN refugee agency says are in a precarious position.