Dave Smith said his 14-year-old daughter Hannah died last Friday after being “cyberbullied” on the question-and-answer website ask.fm, which allows users to send messages to one another without their identity being disclosed.
He is urging the authorities to close down the site, and those like it, after stumbling across cruel taunts from so-called “trolls” which he said drove his daughter to take her own life.
He has appealed to David Cameron to put regulations in place that will protect vulnerable people from online bullies.
Speaking from his home in Lutterworth, Leicestershire, 45-year-old Mr Smith told the Leicester Mercury: “Websites like this are bullying websites because people can be anonymous.
“If I had not spoken up about this, another teenager could be dead next week.
“Ask.fm and sites like these are making millions out of people’s misery and it is wrong.
“I would appeal to David Cameron as a Prime Minister and a father to look at this to make sure these sites are properly regulated so bullying of vulnerable people like my daughter cannot take place.
“I don’t want other parents to go through what I am going through.”
The schoolgirl was found hanged in her bedroom by her sister Jo, 16.
Mr Smith later found a note written by Hannah which read “I wonder if it’s ever going to get better”, the Daily Mirror reported.
Mr Smith, a lorry driver, described his devastation over his daughter’s death.
He said: “We sleep downstairs now, we don’t have a bedtime.
“Since this happened I have only had three hours’ sleep a night.
“I want this to be sorted out as soon as possible so no other vulnerable children die.
“Hannah was a bubbly, happy person.
“She was colourful, she was a normal teenager and was very, very happy.
“For Hannah to do something like this... We never expected this. We never saw any signs of her doing this.
“I have now got to concentrate on burying my daughter. I need to be left alone to bury her and to grieve properly for her.”
Around 20 floral tributes have been left propped up outside the front wall of teenager’s home.
One hand-written card left with a bouquet said: “Rest in peace Hannah. Truly missed. Love all the Johnsons.”
Another said: “Dear Hannah. May you rest in peace little angel.”
Nora Parker, headteacher at Lutterworth High School, where Hannah was in Year 9, said the staff and students were deeply upset at hearing news of her death.
She said: “The governors, staff and students of Lutterworth High School were deeply shocked and saddened to learn the news that on 2nd August Hannah Smith, a Year 9 student, took her own life.
“Hannah, who just completed her final year at the school and was looking to transfer to Lutterworth College in August, was a bright, bubbly, popular and thoughtful girl who was liked and respected by all those she came into contact with.
“She had everything to live for and her family, who are utterly devastated, are at a loss to understand why this has happened.”
Ms Parker said she spoke for the whole school when she said that everyone who knew Hannah was shattered by the tragedy and trying to come to terms with the enormity of what had happened.
She added: “The responses of so many of her friends and teachers to the news of her death emphasises how much she meant to them and how greatly she will be missed.
“Our heartfelt condolences, thoughts and prayers go out to all Hannah’s family and friends at this terribly sad time.”
A Facebook tribute page has been set up for Hannah, called RIP Hannah Smith, and already has more than 19,000 “likes”.
It says on the page: “Hannah Smith; a beautiful young girl who everyone loved very much; who decided to take her own life after being bullied; we will miss you princess; loveyou”
Although people wanting to use ask.fm have to register an email address, name and date of birth, those posting messages can choose to do so anonymously.
Hannah’s death echoes that of 16-year-old Jessica Laney, who was found dead at her home in Florida in December after users on social networking sites tormented her with insults and asked: “Can you kill yourself already?”
Laura Mckay, from Skipton, writing on the Change.org petition set up in Jessica’s memory, said: “I’ve been bullied on ask.fm and been told to kill myself many times. It’s easy for people to hide behind and bully and it needs to be stopped.”
Sharon Sully, from Cumbria, said: “How many more young lives have to be lost before it’s (ask.fm) closed down?”
Philip Parsons, from Southport, wrote: “When does the freedom of the internet become a cancer that destroys lives? Websites like this need to be taken down immediately. The governments need to get serious about the cyber-bullying issues across the globe. RIP.”
Hannah’s death comes amid a growing row about the policing of social media after rape and even bomb threats were made to high-profile female media personalities on Twitter.
Television classicist Mary Beard said yesterday that she has received numerous “threats of violence and death” on the social media site in recent days.
Guardian columnist Hadley Freeman, Independent columnist Grace Dent and Europe editor of Time magazine Catherine Mayer are among other women who have suffered similar threats.
It has led to calls for Twitter to do more to protect users from bullying and even an attempted 24-hour boycott of the site led by writer Caitlin Moran under the hashtag #Twittersilence.