Probably your best bet starting point is a database called eMarketer Pro which is specifically focused on emarketing. You could keyword search, or go to 'Advertising & Marketing' -- 'Social Media' to browse content. There are also relevant statistics in the Statista database wherein you can keyword search or brows by Statistics -- Internet -- Social media. Lastly, the Mintel Reports database has reports on digital media advertising, social media influencers, etc.
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