A customer who has experienced brand's value proposition (for a strong brand), possesses valuable piece of information, which he will share with (i) his closely tie friends to nurture his relationships with them and/or (ii) friends in his broader social groups and may also include their acquaintances, to help them because of his benevolent nature. WOM in (i) case will have strong impact on brand image while in (ii) case WOM will have relative weak impact on brand image. Hence, nature of customers sharing the information plays important role in the relationship between WOM and brand image. To strengthen relationship between low WOM and brand image, marketers may target closely tie friends of customers falling in the second case. Companies may take the help of social media based marketing strategies to identify such customers.
You can refer to the report of Mckinsey even..
MCKINSEY: "A consumer is significantly more likely to buy a product as a result of a recommendation made by a family member than by a stranger… In fact, our research shows that a high-impact recommendation—from a trusted friend conveying a relevant message, for example—is up to 50 times more likely to trigger a purchase than is a low-impact recommendation."