eMarketer has trends and some data, such as CPC ("cost per click).
Provides access to statistics and studies gathered by market researchers, trade organizations, scientific publications, and government sources on over 600 industries.
According to Investopedia, a white paper is generally issued by a company but also a government agency.
Examples of white papers related to Social Media & marketing:
Hootsuite - software that helps communicate between social media channels and provides analytics. The company produces a social media trends paper annually, which may include data.
Accenture - consulting firm which publishes occasional papers on various topics. They have papers on social media as commerce.