Alex Batty disappeared while holidaying in Spain with his mum Melanie Batty, 37, last October.
His grandmother and legal guardian Susan Caruana, 62, said her daughter had previously taken him to live in a Moroccan commune as part of an “alternative lifestyle”.
During last October’s holiday near Marbella, Melanie and Alex sailed from Malaga to Melilla, on the Moroccan border, Greater Manchester Police believe.
The pair were travelling with David Batty, 58. Yesterday was Alex’s 12th birthday.
Detectives and Mrs Caruana fear Alex may have been brainwashed against his legal guardians while in Morocco.
Last night Mrs Caruana, of Oldham, said of Alex’s agreed trip to Spain: “When they were due back, I got this message on Facebook.
“It was a YouTube video of the three of them. They all spoke on it and Melanie said what they had done. Alex said it was a million times better being with his mum and grandad.
“Obviously it hurt me a bit but then my other concerns kicked in.
“They have done this because basically my lifestyle, my belief systems, are not what they agree with. Mine are just simply normal – but they didn’t want him to go to school. They don’t believe in mainstream school.”
She added: “I just want to say to my grandson, ‘Alex, I love you so much. Please get in contact’.”
She added: “We always did something nice with him on his birthday. We’d have a party or go bowling with his friends or trampolining.
“I just hope they do something nice with him today.
“I’m beginning to think I may never see him again. I just die inside a little bit more every day.”
Both Miss Batty – who does not have parental guardianship – and Mr Batty are wanted by police in connection with Alex’s alleged abduction.
Detective Sergeant Pete Morley said: “Alex should be at home in Oldham and there are genuine concerns about his welfare.”
Anyone with information should contact Greater Manchester Police, or Crimestoppers anonymously on 0800 555 111.