One in five teachers have received abuse aimed at them on social media and online forums from parents and pupils – some as young as seven – a survey by the NASUWT union has found.

One teacher about to go on maternity leave was told online by a parent: "My son will fail now because of you."Another discovered a Facebook page set up by a pupil claiming the teacher wanted to kill him. One pupil told a teacher via Twitter: "You are a paedo and your daughter is a whore."

About 7,500 teachers responded to a survey on the use of technology conducted by the NASUWT, which is holding its annual conference in Birmingham.

A majority of teachers who received online abuse did not report it to their employers or police, in many cases because they did not think it would be taken seriously.

Of teachers who did report abuse to school management, 40% said no action was taken against pupils and 55% said no action was taken against parents. Where abuse was reported to the police, more than three-quarters said no action was taken against pupils or parents.

Facebook was the most commonly cited forum for online abuse, followed by the Rate My Teacher website and Twitter. A small percentage reported receiving abuse through YouTube, Snapchat and Instagram.

Of the respondents, 26% said photos or videos of themselves had been posted online without their consent. "We constantly have to trawl through YouTube, Facebook and Twitter for posts and videos," one teacher said.

Teachers reported having fake Facebook profiles set up with sexual comments, while one said a Facebook post in their name stated: "I will rape every Year 8 pupil who comes to the school."

Chris Keates, general secretary of the NASUWT, said comprehensive guidance on schools and internet safety had been done away with by the current government on the grounds it was bureaucratic.

"Teachers are often traumatised by the attacks made on them through social media," Keates said."Schools need policies which prevent abuse and identify sanctions which will be taken against parents and pupils who abuse staff in this way.

"Schools should also be supporting staff in securing the removal of the offensive material from social media sites and encouraging the staff concerned to go to the police."