The process of contacting an online source should online be used after careful consideration of the risks involved. This technique will force the source to either give you more information to identify themselves or to find additional sources to validate their information.
The means in which you directly engage with the source is dependent on how the source contacted you. If you received information via Facebook, you can message the source back asking them to identify the source of what they are reporting. If it was on Twitter, you could tweet the source.
TEST YOUR KNOWLEDGE
Do you think these are the real names and pictures of these people? Why do you think they would use these names?