We analyze the relation between virtual stock holding changes on a social trading platform and stock holding changes of all private investors in a national economy. Our data sources are the social trading platform wikifolio.com and the Securities Holdings Statistics-Base plus (SHS-base) of the German central bank. We find that the transactions of signal providers on wikifolio.com are a good proxy for aggregate transactions of private investors – mirrored by the SHS-base – during the same month, and a good predictor for the aggregate transactions of the private investors in the following month.