Social media was used to track down a Melbourne teenager who posted a suicide note on popular blogging site Tumblr yesterday afternoon.

The young girl was taken to hospital after a Melbourne man used his detective skills to contact her relatives using Linked-In, Twitter and Facebook.

The man, who did not wish to be named, said it filled him with joy to help the young girl.

"This is the best possible outcome. We have had a couple of youth suicides in our family. It's such a tragedy when young people have no choice and feel they have no one to turn to."

He was first alerted to the girl's situation on Twitter at about 2pm yesterday afternoon and knew he had to act immediately.