The visitors made a bright start but Doncaster scored two goals in quick succession in the first half through Billy Sharp and Dean Shiels.
Although Aaron Mclean got Posh back into the match before the interval with a header, Rovers wrapped up the victory late on when Jason Shackell nodded in.
The defeat means Peterborough have won just one match all season and Ferguson said: "I'm the manager and I've got to take full responsibility for the results we've had and I do.
"The players have got to start taking responsibility for the performances as well. But as a group this is nowhere near good enough. We've played 13 games. We've had one win.
"You don't have to be a genius to work that out, it's nowhere near good enough.
"It's got to change and it's got to change quick, I'm fully aware of that."
After Peterborough had pulled a goal back, Mclean saw a penalty appeal waved away when his strike appeared to hit the arm of James O'Connor.
Ferguson refused to blame the referee over the decision, but admitted it could have affected the result.
"The referee has made a decision and he's had to make it quick," he said.
"That's the way it goes. Some you get some you don't. It would probably have had a bearing on the result because we would have got it to 2-2 at half time.
"I feel over the 90 minutes Donny deserved the win."
Ferguson brought on Dean Keates and Lee Frecklington after the interval as he changed formations a number of times, but admits he is desperate to make some signings.
"There's nothing wrong with admitting you need help, but it's got to be the right player," he added. "It's got to be someone that's going to improve the team. At the moment we just can't find the right person."
Rovers boss Sean O'Driscoll was delighted to finally see his side get back to winning ways after they had gone seven matches without a win.
"Every point in this division is precious, so to get three is pleasing," he said.
"We've played much better than that and not got anything out of the game so it's a crazy division.
"We started off a little bit nervously but then we had a purple patch where we scored two goals."