The family of 44-year-old Scottish aid worker David Haines, who is being held hostage by the Islamic State in Syria have pleaded with his captors to contact them. Haines was featured in footage showing the beheading of U.S. Journalist Steven Sotloff where he was held by the Isis militant known as “jihadi John” who reached notoriety during the execution of U.S. journalist James Foley.

His family’s statement says:

We are the family of David Haines.

We have sent messages to you to which we have not received a reply. We are asking those holding David to make contact with us.

Haines has a teenage daughter in Scotland from a previous marriage as well as another child, a four-year-old daughter in Croatia. He has worked for aid agencies in some of the world’s most troubled spots and was abducted in March last year when he was in Syria working for the Agency for technical Cooperation and Development (Acted) to support refugees.

His employer, Acted, also released a statement addressed to his captors:

The threats on David Haines’ life are intolerable.

More than ever, we are pursuing our efforts, and our thoughts are with David and his family.

Acted strongly condemns the violence and threats against David.

A man’s life should never be threatened on account of his humanitarian commitment.

Once again, we call upon the immediate release of David.

The Foreign and Commonwealth Office (FCO) have said that no response by the extremists has been forthcoming so far.