The British Red Cross provides a service to help find missing relatives internationally. It is for families that have been separated by natural disasters, wars or migration. They may also be able to assist if there is a humanitarian need for locating someone.
This is a free service to assist in helping families reconnect. They may be able to help you find those you have no contact with or get a message to family members. Searches are performed by a tracing team with expertise in reuniting families.
To utilise the service, you need to make an appointment at a local branch that provides the family tracing service. A register of all locations in the UK is kept online.