"Even one dollar can make a difference. We’re saying to people: 'For you it's a dollar, for them it's a lifeline'," WFP head Ertharin Cousin said in a statement.
"All it takes is $1 from 64 million people," she said.
The UN agency was forced to make the plea after running out of funds to pay for its food voucher programme for Syrian refugees in Jordan, Lebanon, Turkey and Egypt.
"For refugees already struggling to survive the harsh winter, the consequences of halting this assistance is devastating," it said, adding that the $64 billion (51.8 million euros) was needed "immediately".
It said distribution of electronic food vouchers, which was suspended Monday, was to resume as soon as the pledged cash comes in.
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While WFP didn't name which countries haven't made good on their commitments, foreign ministers from Germany, Finland and Sweden told reporters in Copenhagen this week that their countries could do more to fill the funding gap.
WFP told AFP it didn't want to point fingers at those who had not come good on pledges, saying it did not want to embarrass historic donors who now found themselves in difficulty because of the economic crisis.
More than half of Syria's population has been forced to flee their homes since war began in their country in March 2011.
Some 3.2 million have fled beyond the country's borders, and more than 7.2 million have become internally displaced, according to the United Nations.
There is no end in sight to the fighting in the brutal conflict that has killed nearly 200,000 people.