Pretty creepy. Being concerned for a family member or close (IRL) friend is one thing. Marshalling an Internet horde because someone stopped checking in on Github is entirely another. If you only know someone by their @ handle, then you don't know them well enough to start investigating their lives. I get that some people don't have an IRL to contrast their virtual presence with, but that's a pathology, not an invitation to stalking. Once more from the top: If someone doesn't share his or her contact information with you, then it's very likely they DON'T WANT YOU CONTACTING THEM, much less organizing a them-themed flashmob. Jesus.