Syrian tanks were closing in on the rebel-held town of Qusair last month when a Kuwaiti sheik named Hajjaj al-Ajmi and his money machine roared into action. In a series of urgent messages on his Twitter account, al-Ajmi appealed for cash to help save the town's defenders.

"I hope that we can be a means for helping them and relieving them," the young cleric wrote to his 250,000 Twitter followers on May 25. He gave a phone number for making donations and asked readers to "kindly spread it."

The appeal came too late for the rebels in Qusair, but the technique has proved remarkably successful for al-Ajmi and a handful of other private backers of Syria's patchwork of rebel groups. In just over a year, al-Ajmi's foundation has raised hundreds of thousands of dollars to finance Syrian rebel groups.