Hibu spearheaded an anti-trafficking drive last year and handled the case of a girl from the remote northeastern state of Arunachal Pradesh who had befriended a man on Facebook.
He bought her an air ticket to Mumbai, where he sold her into a brothel.
"She was a high school student, very poor. But she had a smartphone with internet. This is a hidden tsunami. Today mobile phones are not that costly," said Hibu.
India is only the latest country to experience the grim phenomenon - all over the world, concern is growing over the use of technology by traffickers, who use social media to contact vulnerable teenagers before selling them into sex work.
But with internet penetration at just 18 percent in rural areas, according to a report from the Internet and Mobile Association of India, there is still huge scope for growth.
The report said mobile internet was predominantly used by young people, with 46 percent of urban users and 57 percent of rural users under the age of 25.
Payments too have gone online, eliminating the money trail, according to Cassandra Fernandes of anti-trafficking charity International Justice Mission.
"Earlier, traffickers visited the family, convinced them about a job prospect in the city ... they were usually people the family trusted," said Vivian Isaac, programme director of the My Choices Foundation which works with women and girls.
"Now they sit in their rooms and send messages on Facebook and WhatsApp and girls walk into their trap themselves. They never show hurry. They do it gradually, systematically."
For families of migrant workers, the mobile phone is their only connection to their loved one.
Tanu now plans to change her number - but says she will keep her smartphone.
