Less literal, but a fairly common expression in English marketing texts.

Conceptually, I think it conveys the idea: alcance = potential in this case, and propagação = word of mouth in the sense of promotion, dissemination, spreading.

Some examples:

Measuring Word-of-Mouth Marketing
www.nmincite.com › InsightsApr 2, 2010 – ... an effective marketing vehicle, companies need to outperform on product and service attributes that have intrinsic word-of-mouth potential...

McKinsey Studie Word of Mouth Marketing
www.slideshare.net/.../mc-kinsey-studie-word-of-mouth-marke... consumers into an effective; 8marketing vehicle, companies need to outperform on product and service attributes thathave intrinsic word-of-mouth potential...

Referral marketing - Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/Referral_marketing Referral marketing is a structured and systematic process to maximize word of mouth potential. Referral marketing does this by encouraging, informing, ...