The micro blogging site posted revenue of $502m, up 61% year-on-year and beating its own top forecast of $485m.
But active users reached 316 million in the period, up only slightly on the 308 million in the first quarter.
Mr Dorsey said the firm had to do more to realise its full potential.
"We've got unbelievable brand awareness, but people are not clear why they should use it themselves," he said.
The bulk of new active users came from the social network's SMS fast followers - people who sign up for text alerts but don't need a Twitter account.
Excluding these active users rose by just 0.7% compared to the previous quarter.
Speaking after the results, chief financial officer Anthony Noto said the firm would start a marketing campaign aimed at addressing why people should use Twitter by the end of the year.
He said it would also simplify the service to make it easier to use.
But Mr Noto warned that the firm did not expect to see  "sustained meaningful growth" until it reached a mass market audience, which he said would take a "considerable period of time".
MCH analyst James Cakmak told the BBC that both Twitter executives were "extremely candid, more than any of us expected".
"There's clear evidence of a focus that wasn't there before. They gave comfort about their strategic direction," he added.
But he said the fact there was no update on the appointment of a permanent chief executive was concerning.
Mr Dorsey took the helm temporarily at the start of this month after previous boss Dick Costolo stepped down.
The change came after pressure from investors unhappy with the firm's user growth.
The number of Twitter users is still dwarfed by its most high-profile competitor, Facebook, which boasts 1.4 billion users.
And analysts remain sceptical about its long term prospects for increasing active users from its current niche user base of celebrities and journalists.
Investors' initial reaction to the second quarter results was positive, with shares rising over 6% in after-hours trading, before falling sharply to trade 6% lower at $34.24.
Shares in the social networking site, which have fallen around 10% over the past year, are still below the $38.80 price they debuted at on the stock market in 2013.
The firm, which has yet to post a profit, also reported a smaller than expected loss of $137m for the period.
Twitter said it expected full year revenue of between $2.20bn to $2.27bn, slightly higher than its previous forecast.
Twitter's revenue and earnings for the second quarter have beaten expectations, but co founder Jack Dorsey has said he is "not satisfied" with its user growth.