EU foreign policy chief Javier Solana says EU officials have been doing all they can to try to establish the whereabouts of the BBC's Alan Johnston.
He has been missing for a week and is believed to have been abducted in Gaza.
Mr Solana said from the first day the EU had been talking to Palestinian leaders and figures from civil society to try to see if he could be freed.
The BBC has again appealed to everyone with influence to intensify efforts to ensure Johnston's quick release.
"We continue to work tirelessly with the authorities in Gaza and elsewhere to try to locate Alan," the BBC said in a statement on Tuesday.
"However, despite the assurances that we've received about his welfare, we still do not have any firm knowledge regarding his condition or his whereabouts."
The BBC also expressed thanks to all who showed their support at demonstrations in the UK and the Middle East on Monday.
Mr Solana told the BBC: "I can tell you that from the very first day we have been doing the utmost, talking to all the leaders, from the Palestinians and to some friends, [and in] civil society that I know and he knew, and to try to see if we can liberate him - the sooner, the better.
"I don't have any specific information to be made public now, but the other thing I would like to insist on once again is that we are concerned, that we keep on doing all our efforts every day," he said.
On Monday, Johnston's father, Graham, appealed for information and urged anyone holding his son to "just let him go", saying he was a friend to the Palestinian people.
Alan Johnston has been the BBC's correspondent in the Gaza Strip for the past three years - and the only foreign journalist from a major media organisation based in Gaza.
The BBC describes him as a highly experienced and respected reporter.
Aged 44, he was born in Tanzania and educated in Scotland.
He joined the BBC World Service in 1991 and has spent eight of the last 16 years as a correspondent, including periods in Uzbekistan and Afghanistan.
His Gaza posting was due to come to an end at the end of next month.