Read more: Spencer - EU referendum must not be rushed
"I will not give time lines and deadlines and a running commentary on the referendum plans," he told reporters during a press conference after talks with EU leaders.
Business leaders have urged the government to avoid market uncertainty by doing the referendum as soon as possible. Last week Bank of England governor Mark Carney said a referendum should be held "as soon as necessary".
Today's talks were designed to focus on eastern European countries, but Cameron said the meeting, between the leaders of Europe's largest countries and their eastern counterparts, had provided an opportunity to gauge other leaders' views on the UK's relationship with the bloc.
"I'm not going to say I was met with a wall of love when I arrived," he said. But he added that his counterparts were "not happy with the status quo and neither am I".
But Cameron insisted he would push hard to renegotiate the UK's relationship with the EU.
"I think our leaders can see that there has been an election and the EU should see that Britain has a mandate for changes."