Posters of two children missing for more than a year from their Scottish home are to be put up in Spain where it is feared they may have been taken by their fugitive father.

The charity Missing People plans to distribute the posters of Rhianna Turner, eight, and her brother Charles, nine, who have not been seen since last June after they failed to turn up at school in Edinburgh.

It has also posted photographs of the two children on its website, while fellow missing persons organisation Forever Searching is expected to send out information across social networking sites.

The groups came forward in response to an appeal for help by Lothian and Borders Police at the weekend. Two reported sightings of the pair in Glasgow by members of the public following the appeal proved to be mistaken identity.

Police suspect the youngsters have been taken abroad by their father, also called Charles Turner, 34, who is wanted on several outstanding warrants after failing to appear at Edinburgh High Court on drugs-related charges in January.

Although school staff notified education authorities at the time of the pupils' disappearance it is understood that the case was only reported to police in February because the travelling family was known to come and go.

Relatives, including the children's mother Maureen Shaw, who is estranged from Mr Turner, have repeatedly claimed that the children are safe and well but they refuse to say where the brother and sister are, leaving the authorities worried about their wellbeing.

Constable Fiona Gilchrist, inquiries officer at Dalkeith Police Station, said the charities efforts were "fantastic".

Referring to the two negative sightings, she added: "Unfortunately the descriptions were of children who were younger than the children we are looking for."

The children's headteacher is understood to have reported their disappearance to Edinburgh City Council just before the 2007 summer holidays. Anyone with any information should contact Lothian and Borders Police.