Conversation so far:
How was Walter Winchell's professional career start?
He left school in the sixth grade and started performing in Gus Edwards's vaudeville troupe known as the Newsboys Sextet, which also included George Jessel.
How did Walter Winchell do with the troupe?
He began his career in journalism by posting notes about his acting troupe on backstage bulletin boards.

Question: What media outlet he joined to do this?
Self-contained rewrite: What media outlet Walter Winchell joined to post notes about his acting troupe on backstage bulletins boards?