Jack Letts left his home in Oxford to travel to the war-torn country a year ago.
His mother, Sally Letts, has insisted that he left for humanitarian purposes rather than terrorism.
The former books editor told the 'Evening Standard', "He is not a member of ISIS; he is very probably not the first white convert that has gone out there. We spoke to him yesterday and he said he had never had a weapon in his
She conceded that the family, based in Oxford, are concerned for Jack's well-being.
"We are worried sick. He is in danger every single moment of the day. He is very naive, very misguided. He wanted to do good in the world and wanted to see for himself. The fact is he did not see the danger or think about his own safety. We wake every single morning not knowing whether he is alive or dead," she told the newspaper.
Jack told his mother and father John, a leading organic farmer, he was planning to travel to Kuwait to study Arabic.
He only informed them he had subsequently gone to Syria once he arrived. He initially worked with refugees and most recently has been helping in a hospital, his family said.
"He repeatedly said he is not with IS, and he does not lie. He believes it is un-Islamic to lie and if he does he will go straight to hell, so there is no doubt whatsoever. He has worked in a hospital, done some teaching, done some translating. He is integrated with the population," Sally said.
