His plea comes as Scottish Executive statistics show a continuing fall in adoption applications.
Last year there were 400 successful applications - 50 fewer than in 1999.
Of the total applications, 44% were for children aged under five compared to 37% in 1999, when a higher percentage of applications were for five to 11 year olds.
The figures found just over half of all applications were made without using an agency, while those made through a council accounted for 36%. The proportion of applications made through voluntary agencies increased to 12%.
'There are many vulnerable children in Scotland's care system,' said Mr McConnell. 'For too many years there has been a declining number of adoption applications and less children are being placed. Modernising the system will help us change this.'