Nine doctors and medical students are believed to have travelled to Syria, to work in ISIS controlled hospitals, the BBC reported.
The group of four women and five men were all born and raised in England, but were going to medical school in Sudan's capital, Karthoum. They are believed to have travelled to Syria over a week ago.
Their families are reported to be very concerned about their welfare. Some of the teenagers' relatives travelled to the Turkey-Syrian border in an effort to persuade them to come home, according to The Guardian newspaper.
"We all assume that they are in Tel Abyad now, which is under ISIS control. The conflict out there is fierce, so medical help must be needed," Turkish opposition politician Mehmet Ali Ediboglu told The Observer, shortly after meeting the families.
The British government said that if the young doctors decide to change their minds and return home, they will not face criminal prosecution, provided they were not involved in fighting activities.
"UK law makes provisions to deal with different conflicts in different ways -- fighting in a foreign war is not automatically an offence but will depend on the nature of the conflict and the individual's own activities," a government source told The Guardian.
One of the youngest in the group, 19-year-old Lena Maumoon Abdulqadir, sent a brief text message to her sister shortly before crossing the border into Syria, saying she wanted "to volunteer to help wounded Syrian people."
The case follows the disappearance of three London schoolgirls last month, who police believe crossed into Syria from Turkey.
Turkish authorities criticised British police for taking three days to alert them to the missing schoolgirls.