The Church of Scotland should aim to find 100,000 new members by 2025, according to the Moderator of its General Assembly, Rt Rev John Chalmers – and cyberspace is a potential recruiting ground.

Writing in a new year message to be published in the Church's Life and Work magazine, Chalmers argues that membership should be redefined to become more representative of the real situation in churches. He says: "I am fed up with the Church of Scotland publishing annual statistics which highlight a decline in membership when the truth about the number of people who belong to our faith communities is, in reality, quite different. I want, therefore, to open the New Year with a very serious challenge for the Church of Scotland."

He argues that the Church needs to "redefine membership in a way that allows us to include women and men, young and old who do not fit the post-second world war model of membership with which we are so familiar."

Chalmers continues: "I'm looking for a way of including the many hundreds of people who are fully engaged in the practical and project work that our churches are doing throughout Scotland, but whose belonging to the faith community is not necessarily complemented by regular attendance at Sunday worship."

He says that discipleship "needs to be made possible using the computers, tablets and telephones that are now a near extension of ourselves" and that he was "proposing a conversation about how these ubiquitous tools can be used to foster the inclusion of those who, while they may well be converted to the Christian faith, may never be converted to use its sacred spaces and dedicated places in the same way as I do".

However, the initiative was criticised by the Moderator of the Free Church of Scotland, Rev David Robertson, who said that it represented "sleight of hand" with numbers and that active membership in the Church of Scotland was far lower than the 400,000 figure usually quoted. "There are many instances of a church with a membership of 1,000 where only 100 attend," he said.

He argued that widening the criteria for membership was the equivalent of adding 'Facebook friends' and would give an even more over-optimistic picture of the Church.

"The Church needs to move beyond trying to retain its status and genuinely reach out," he said. "If it only has 100,000 active members, that's a great basis on which to do real, proper outreach."

Robertson warned that some committed Church of Scotland members were leaving because of its support for same-sex unions.

A proposal by the General Assembly to allow congregations to decide for themselves whether to appoint ministers in a same-sex relationship reached its target of more than 50 per cent of presbyteries voting in favour last week, according to the Aberdeen Press and Journal.