The hashtag campaign for the Nigerian girls — originated in Nigeria by Nigerians — was meant to do exactly that: pressure the Nigerian government to respond more seriously to the kidnapping. It has already had this effect. And attention from abroad has helped magnify the pressure.
As always, however, we tend to romanticize the power of the tweet. For a while, Twitter (and other social media) was seen as a game-changer that would empower the masses and invert the age-old relationship between the ruler and ruled.
This is mostly rubbish. Yes, the tweet improves upon the mass petition because tweets contain an instant return address that allows for mass mobilization. People can be summoned to gather together somewhere — Tahrir Square, for example.
At which point, alas, the age-old dynamics of power take hold. If the tyrant, brandishing guns and tanks, is cruel and determined enough, your tweets will mean nothing. Try it at Tahrir or Tiananmen, in Damascus or Tehran. They will shoot and torture you, then maybe even let you keep your precious smartphone.