The 52-page report by the comptroller and auditor general, said that although Mas was achieving value for money for its provision of debt advice, evidence was mixed that the site was meeting consumer needs for generic money advice.
The NAO’s report warned that Mas was not doing enough to engage with consumers who did not have access to the internet and promote its phone or face-to-face channels.
It added that Mas had not, to-date, “sufficiently targeted its interventions to those who need it most”.
While the proportion of consumers using tools such as savings calculators and budget planners on the website had increased between June 2012 and July 2013, the amount of time spent on the site had fallen in the same period from an average of four minutes and 10 seconds to two minutes 39 seconds.
The report also criticised Mas’s failure to complete the development of its mobile internet platform.
Caroline Rookes, chief executive of Mas, said: “We look forward to working through the recommendations of the NAO in the months ahead and using them to further improve our service and, as a result, provide long-lasting help to our customers.”
Mas came under fire last week in a 41-page Treasury select committee report that raised concerns it was duplicating existing services and not achieving value for money.
Mas provided 158,000 face-to-face debt advice sessions in 2012/2013, an increase of 58 per cent on the previous year.
More than 2m consumers used the Mas website in 2012/2013.
The Mas phone, webchat and face-to-face money advice channels were accessed by 195,000 people.
Visits to the website increased by 400 per cent in the wake of an £18m marketing campaign.
Keith Macdonald, certified financial planner for Worcestershire-based Broadway Financial Planning, said: “Mas is a bit of a misrepresentation. It’s more of an information service and is not something that can easily help someone build wealth.”