NEW DELHI/LONDON (REUTERS) - German development worker Caroline Siebald and her boyfriend Charles Gertler, an American glaciologist, were on a rafting trip in Nepal when the earthquake struck and initially panicked about how to let their families know they were safe.
After about 30 attempts, Gertler, 25, managed to get a phone call through to his mother in Massachusetts in the United States, and she registered them as safe on Facebook's "Safety Check".
Within minutes, their friends and families saw the news.
"I had messages from my best friends in kindergarten saying'Oh my God, I'm so glad you're alive'", Siebald, 22, told the Thomson Reuters Foundation.
From migrant Nepali domestic workers in India to IT professionals in Brazil, people across the globe have taken to social media sites such as Facebook and Google to look for missing relatives and pass on news of survival in Nepal.
In India, which has the highest population of Nepali migrants in the world, many have been frantically trying to phone home, horrified as they watch television pictures showing bodies being pulled out of the rumble of collapsed buildings.
"I don't know anything about my son who is in a village with my parents far from Kathmandu. I am calling on the phone all the time, but I can't get through. I can't eat, sleep or work," said Usha Tamang, a nanny of Nepali nationality working in Delhi.
Elsewhere in the world, others are searching for relatives and friends who were visiting the Himalayan nation during its peak tourism season.
An estimated 300,000 foreign tourists were in the country, several hundred of whom were on Mount Everest, when Saturday's 7.9 magnitude quake struck, killing more than 3,800 people.
The International Committee of the Red Cross (ICRC) was one of the first agencies to launch an online platform to trace the thousands of people who are missing.
The family tracing service publishes lists of names and information on people who are safe and well, hospital patients, people who are looking for relatives, sought persons or those who are dead.
Individuals can access these lists directly on the webpage to look for the names of their family members or register themselves as safe or in danger.
Facebook has also launched its Safety Check tool https://www.facebook.com/safetycheck/nepalearthquake for Nepal, drawing praise from Facebook members.
"It's a simple way to let family and friends know you're okay. If you're in one of the areas affected by the earthquake, you'll get a notification asking if you're safe, and whether you want to check on any of your friends," Facebook CEO Mark Zuckerberg posted. "When disasters happen, people need to know their loved ones are safe. It's moments like this that being able to connect really matters."
An IT professional in Brazil was one of many who said that the initiative had helped her trace her family.
"My father and friends are in the area and one of the first contact points we had to get some news was Facebook. This media is not always about likes and fun," the woman wrote in response to Zuckerberg's post. "When you or someone in your family is in danger, you'll try ANY kind of contact and I'm glad Facebook helped me today. Connection is what matters."
Another application, the Google Person Finder https://google.org/personfinder/2015-nepal-earthquake/, first launched after the 2010 Haiti earthquake, uses SMS to allow anyone to search or update information on missing people.
On Saturday Jacqueline Brown registered Angus Brown, 46, from London, as safe.
"Angus has emailed, he is in Lumboche with Martin," she said. "Both are fine, warm and have food."
The service is currently tracking about 5,800 people.