Susan McPherson talks about the impact of hashtag activism. Hashtavism as she calls it are posts with a social or political cause filed with a hashtag. Hashtag activism can have a great impact, but it does have to be paired with real-world activism to be effective. Hitting the re-tweet button doesn't do the trick.
Widely spread examples for political hashtags are #ArabSpring, #OWS for Occupy Wall Street or #Kony2012. McPherson also names some popular hashtags for female hashtivism such as #BanBossy, #Leanin, #changetheratio or #GirlRising.
Twitter can give a voice to the voiceless. However, you should step up to the plate and back your tweets with actions that go beyond mere tweeting. That makes the difference between real activists and slacktivists.