#BringBackOurGirls: Michelle Obama praying for missing girls

Michelle Obama on Wednesday expressed sympathy for the more than 200 schoolgirls abducted in Nigeria, in a personal message on Twitter.

"Our prayers are with the missing Nigerian girls and their families. It's time to #BringBackOurGirls," said the US First Lady on her @FLOTUS account, with a picture of her solemnly holding a sign saying #BringBackOurGirls" scribbled in black on white paper.

The tweet was signed "mo," meaning she wrote it herself, and it was retweeted more than 8,500 times in just a few hours.

President Barack Obama on Tuesday called the mass kidnapping three weeks ago by Boko Haram Islamists "heartbreaking" and "outrageous."

The US has sent experts including from the military in the hunt for the girls, who were snatched at gun point from their Nigerian school.