"The worst thing is not knowing, the worry and the headaches and the not sleeping, just thinking about your boy."

Kevin Atwood has been living every parent's nightmare. He knew his son, Bryce Lambert, 25, was in Nepal when Saturday's massive earthquake struck, killing more than 4000 people and injuring thousands more.

But in the wake of the disaster, Mr Atwood heard no word from his son, who grew up in Sydney but who had been living and working as a landscaper in Melbourne before his holiday. The silence was agonising, Mr Atwood said.

Was the fact that his son had not been in touch a result of severe disruption to the communication network in Nepal? Or had he become a casualty of the country's worst earthquake in 80 years?

Mr Atwood was among the thousands of people scouring online databases and websites desperately seeking information, however small, about missing loved ones.

The International Committee of the Red Cross has set up a family link website, where people can register names of missing relatives. Google's charitable arm, Google.org, has established another searchable database of missing people, while countless Facebook pages have popped up with people sharing information.

One page, called Langtang Missing/Found People, shows just how social media is helping to fill the information vacuum surrounding the disaster.

A woman who was evacuated by helicopter from Langtang, a remote area of Nepal near the Tibetan border, had asked those also isolated in the village to write down their names in a notebook before she left.

Photographs of those names, separated into nationalities, were then posted on Facebook. It was often the first time family and friends knew that their missing loved ones were alive.

"THAT'S MY GIRLS !!!!!!!!!!!!!!!!," responded a family member of Australian woman Athena Zelandonii, who had been reported missing until that point.

Mr Atwood had registered his son missing on all the websites.

On Tuesday morning, he received the message he had been desperately seeking since Saturday: his son was alive and staying at a school on the outskirts of Kathmandu.

"I still haven't spoken to him at this stage, the communication is very poor over there, but we have received a message to say that he is okay," Mr Atwood said.

He learned that his son had been rockclimbing when the earthquake struck, and now was trying to help in the relief effort.

Mr Lambert had originally planned to be at Mount Everest base camp on Saturday, when the earthquake struck, but bad weather had postponed his trip for several days, and he then decided to abandon it altogether. At least 19 people, including Australian woman Renu Fotedar, were killed when an earthquake-triggered avalanche hit the camp.

"I never want to go through that again," Mr Atwood said.

"I had just left a message on my son's Facebook page, saying "Where the bloody hell are you son? We're sick of worrying about you. PS. You're grounded."