Redknapp stepped down from his post at Loftus Road on Tuesday, with the London club second-bottom in the Premier League.
The former West Ham and Tottenham boss cited imminent knee surgery as the reason for his departure, although the pressure had been mounting on Redknapp, who had seen his side lose all 11 of their away league games this term.
Ahead of Saturday's visit of Southampton, Ramsey - who will take charge with Kevin Bond - has demanded a response.
"It's always a surprise when something like this [Redknapp resigning] happens. It was a shock, a big surprise," Ramsey said.
"The players really need to step up now and achieve what they're capable of.
"We need to be on the front foot, giving maximum energy and showing some flair. We need to get fans off their seats."
With the business end of the season drawing closer, QPR will be keen to resolve their managerial situation swiftly as they seek to push for top-flight survival.
However, Ramsey revealed the club have not set a timeframe for appointing a replacement.
"I'm in this role with Kevin Bond to steady the ship until the club appoints someone to take the role," he added.
"There's no timeframe, as far as I am aware, for the new appointment.
"It's down to the owners to decide who they think is the best fit for the club. They will decide who is the best for QPR."
Former Tottenham boss Tim Sherwood is the odds-on favourite to succeed Redknapp on a permanent basis.
