Russia and Ukraine are in talks to secure a deal to end their gas dispute, months after Russia's Gazprom cut supplies to the ex-Soviet state.
Merkel spoke in Bratislava after meeting Slovak Prime Minister Robert Fico, who reaffirmed his opposition to offering Kiev any financial assistance.
But Merkel said: "Everyone must contribute, including Slovakia.
"We're looking for a solution now, we don't have one yet and winter's already coming."
She said it was important for the European Union, Russia and Ukraine to reach a solution "that will help stabilize gas supplies this winter".
The EU will on Tuesday host gas talks between the countries in Brussels with the goal of securing a deal to end the dispute.
Gazprom cut deliveries to Ukraine in June after Kiev disputed a price increase set by Moscow.
Ukrainian President Petro Poroshenko on Sunday said he and Russian counterpart Vladimir Putin had reached a price deal on Friday at talks in Milan that focused on the six-month pro-Kremlin revolt convulsing Ukraine's separatist east.
Slovakia, which is heavily reliant on Russian gas, has been pumping natural gas to Ukraine at the European Union's behest.
In recent weeks it has seen its deliveries of Russian gas plummet by half of contracted volumes, though Gazprom has denied any reductions.
"Sometimes I get the impression that Ukraine expects the solution to its problems to come from every country expect itself," Fico said at the press conference with Merkel. "Ukraine needs to reform, just as Slovakia once did."