The effect on their friends and family can be dramatic. Youth workers need to know what to do and where to go. Follow this guide and do the right thing.
1 Any missing under-18 is classified as vulnerable. So the police will need to be informed. The police have the resources to search and find young people across the country. They will also work with experienced charities and voluntary groups.
2 Don't assume that getting the young person back home is the priority.
The main thing is to get them safe. Young people might be sleeping rough or staying with someone they have just met. Both conditions put young people at high risk of being abused.
3Don't panic. Most children and young people who go missing are found within 72 hours. It is rare for them to be abducted. Most of the 583 abductions last year involved a child being taken by one of their parents in a custody dispute.
4Talk to the right people. The National Missing Person's Helpline (NMPH) offers a confidential telephone helpline. Message Home allows them to talk to a sympathetic voice. They don't have to say where they are and they won't be preached at to return. They will get help and support to find a safe place and to get a message to friends or family. Calls are free, lines open 24-7, and the phone number is in all UK phone boxes. It is 0800 700 740.
5The NMPH also offers a service to advise families and friends. That includes youth workers. You can call with information or to ask advice.
The charity has had good success with various schemes to trace people, including the Big Issue magazine (pictured), posters, TV and radio, milk cartons and Teletext. Call 0500 700 700 or visit www.missingpersons.org.
6Friends of the young missing person sometimes know where they are but are too scared to say. Give out the Message Home number so they can pass it on. Missing young people often receive text messages or mobile calls from selected friends.
7 Prevention is better than cure. Watch out for signs and talk to young people before they go missing. Young people often leave home when they find themselves in a vulnerable situation, says the charity Get Connected.
So let young people know who can help. Get Connected runs a helpline from 1pm to 11pm every day, and gives young people a chance to explore the options available. It is free to call Get Connected on 0808 808 4994.
8 Once a missing young person returns, there could still be a lot of work to be done. Be alert and sensitive to their needs. Some young people, especially those in care, run away more than once. Again, make sure they know what specialist help is available.