influencer
General Definition:
"One who exerts influence : a person who inspires or guides the actions of others"
More Applicable Definition
"A person who is able to generate interest in something (such as a consumer product) by posting about it on social media"
via Merriam-Webster
influencer marketing
Most Applicable Definition
"A form of marketing in which places focus on influential people rather than the target market as a whole. It identifies the individuals that influence potential buyers and orients marketing activities around these influencers."