The drop is on a par with the 12% decline suffered by rival Northcliffe in the period from the beginning of the year to 28 March. Another regional publisher, Trinity Mirror, is due to provide a first quarter trading update on Thursday (12 May).
Johnston Press experienced bigger declines in ad revenue in the first quarter than the second half of last year, when it was down 5.4% (on a like-for-like basis).
The Yorkshire Post publisher said the rate of decline for the first five weeks of the second quarter, which included Easter and the Royal Wedding, was 7.8%.
Employment was the weakest performing advertising category, due to public sector cutbacks, falling 30.7% in the first quarter.
Display advertising fell 7.9% in the first quarter, but rose 5.5% in the first five weeks of the second quarter.
The target of £5m additional savings is on top of a previously announced £10m savings target intended to offset the higher costs of newsprint.
The savings will be achieved by making back office functions more efficient and will not impact editorial or customer-facing roles, according to a spokesman.
Despite the declines, the company expects its full-year results to be in line with current market expectations of around £27m in pre-tax profits.
The company has not made any progress in reducing its debt, which stood at £388m at the end of 2010 and is now £388.7m.
There was no update on the company's search for a new chief executive to replace John Fry, who announced in March that he would step down.