The regional newspaper publisher's pre-tax profit for the period ending June 30 also dropped 18.1% to £62.5m, down from £76.3m during the same period the year before.
It suffered a 9.5% drop in overall ad revenues, despite digital ad revenues growing by 52.1%.
Total UK-based print advertising for the six months fell by 11.3% and was down 17.2% in June.
Johnston Press warned that ad revenues have continued to decline in the second half of the year and are down 21% after the first seven weeks.
The company took an impairment charge of £109m against the value of goodwill and publishing titles.
Tim Bowdler, chief executive, said: "Advertising trends have continued to deteriorate over the course of the year and future performance will inevitably be linked to the economies of the UK and to a lesser extent that of the Republic of Ireland.
"In response to the current challenging circumstances, we continue to actively manage our cost base to achieve productivity gains and in a manner which will protect the long-term prospects of the group. We expect to deliver a result reflective of these initiatives and the difficult market conditions."
Johnston Press publishes 18 daily newspapers, including the Yorkshire Post, and about 300 weekly newspapers.
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