This is a really interesting question when you think about the rebellions Facebook has been a part of recently. In cases like those, Egypt for example, I don't think you can really say Facebook helped with tolerance!
In general, yes, as with anything, social media can be used for good and bad. If you use it to connect with people around the world who come from different backgrounds and cultures then it can be a great tool.
However, it doesn't seem to me like today's youth is doing this. We hear more stories of bullying and suicide due to social media then you do of kindness.