For one young Swiss man looking for his birth family, official channels had turned up nothing. So Marco Hauenstein, 19, turned to Facebook to try to find out more - not anticipating how widely his post would be shared.
Marco did not have an easy start in life, as the very few facts he knows about his birth mother indicate.
Gina Barbara Hauenstein was a drug addict, and during the 1990s spent time, Marco believes, in Zurich's then notorious Platzspitz open drugs scene, where addicts bought heroin in a city centre park, and injected it openly.
When Marco was born in 1997, he was already addicted too, and had to spend the first months of his life in hospital withdrawing and recovering.
Although his mother visited him from time to time, he never lived with her. About his father, he knows nothing: on his birth certificate, the space for the father's name has been left blank.
Missing mother
In 2000, Gina Hauenstein disappeared. Despite a police search both within Switzerland and across Europe, no trace of her has ever been found, and she remains listed as a missing person.
Image caption Gina Hauenstein: Missing since 2000
Marco meanwhile lived with a foster family. He describes his childhood as happy, but he admits questions about his birth family were "always on my mind".
When he turned 16, Marco left his foster family. There had been disagreements, not unusual between parents and teenagers, but Marco says his relationship with his foster family is good, and has improved since he began to live independently.
Fruitless search?
At the same time, he started to look for his birth family, and in particular for his mother. "I really wanted to know, for myself, who was my family, who I belonged to," he explained.
"So, when I was 16, I started to call town record offices, and I contacted the police. But without success."
Image caption Marco Hauenstein's search has drawn in many social media users, including journalists
Talking to Marco, it is not entirely clear why this more traditional search for family members was unsuccessful. Switzerland is a small country, Marco was never adopted, he knew his birth name, his mother's name and, it seems, the town she came from, where her parents (his grandparents) still apparently lived.
Social media
Perhaps the idea of a Facebook appeal seemed the most logical, or the fastest, way to reach out. And posting messages on social media might understandably be easier for a teenager than cold-calling official figures in local government or the police.
But the simple message which appeared on Facebook just three weeks ago has had consequences Marco - who uses the name Marco Julius Schelling on Facebook - did not expect. His message was shared and re-shared across Switzerland and Germany many thousands of times, and soon the media took an interest in his story too.
Excerpt from Marco's Facebook appeal:
Dear friends, acquaintances & fellow human beings
My name is Marco Hauenstein, and I was born on 17.06.1997 in the Aargau/Zurich region. After going through drug withdrawal as a newborn for 3-6 months I grew up with the Jung family, and later with the Schelling family.
After searching for many years without success, I'm turning to you. I'm looking for my birth parents / grandparents!
When I meet him in Zurich, he seems rather overwhelmed by the attention. He is accompanied by a camera crew from a local television station, and during our conversation he fields calls from a German channel, and a Swiss newspaper. At the same time new responses to his Facebook appeal are appearing on his phone every couple of minutes.
"I've had thousands and thousands of messages," he says. "I really didn't expect this."
Image caption Marco Hauenstein as a baby, with his birth mother
Initial success
But his Facebook search has had some initial success. An aunt, a half-sister of his mother, has reached out to him, he says, and he has talked to her by phone.
"It was very emotional, we didn't talk much, it was just, 'Hello, so good to talk to you after all these years'." The plan is "that we will meet tomorrow… I think we will meet tomorrow".
Marco has also received information relating to his grandmother, an uncle, and even, he says, some hints about the identity of his father. But he seems reluctant to share too much detail. When our interview finishes, he is met by yet another television crew.
Image caption Messages for Marco keep pouring in
Media spotlight
The next day, I get a message from Marco. The planned meeting with his aunt has not taken place, he says, because "I could not reach her".
It is clear the social media attention, and then the interest shown by the mainstream media, have caused problems.
Adopted or foster children hoping to meet their birth families, or birth parents looking for their children, are generally advised to proceed using an intermediary, to communicate in confidence, and to arrange a face-to-face meeting only when all sides are really ready for it.
The advent of sites like Facebook has changed that. Social services report growing numbers of cases in which adopted or fostered children, or parents who have given their children up or had them taken into care, have been tracked down and contacted out of the blue. The brutal reality is that these contacts are not always welcome: not everyone wants a reunion.
Image caption Tracing relatives is difficult for Marco despite the power of social media
Happy ending?
But for Marco, the hopes for a happy ending seem at least partially fulfilled. One day after the failed meeting with his aunt, another short post appears on his Facebook page: "On Friday I was able to meet my grandmother and my uncle," he writes. "It was a very moving moment, at last I have got a part of my family back!"
His aunt, he continues, "needs more time" before agreeing to meet him.
Time will tell if the reunion brings Marco the sense of completeness he feels he needs. His mother remains the key person he wants to find. But there has been no trace of her for 17 years. No one, not the police, the local authorities, nor Marco's new-found relatives, has any clue where she might be.
Marco is not deterred. His search, via Facebook, continues.
By Imogen FoulkesBBC News, Zurich