Back in August, we gave American Express kudos for a social campaign that tapped into artist influencers to up social engagement, and the brand used the same formula in November to create another successful effort. Their #MyAmex campaign gave six popular Instagrammers access to their account to post images that show how Amex impacts their businesses. According to the brand, the posts generated 10 million impressions in two weeks, and generated 23 percent more engagement than the brand's other Instagram pictures thanks to guest photographers. (Adweek)