For marketers who want to know the value of social media and mobile to their brands, the answer is a resounding “very.” A whopping 38 million people, ages 13 to 80, said social media influences their purchasing decisions.

That number is up 14 percent over the last six months, according to Knowledge Networks, which released the results of a recent social media/mobile study.

Among the study’s findings are that teens and adult social media users in 2011 reported high levels of influence:

• 23.1 million discover new brands or products through social media (up 22 percent from 2010);

• 22.5 million use social media to learn about unfamiliar brands or products (up 9 percent);

• 17.8 million are strongly influenced in their purchase decisions by opinions in social media (up 19 percent);

• 15.1 million refer to social media before making purchase decisions (up 29 percent)

Social media use is also increasingly becoming mobile. Forty percent of teens and adults who used social media are now accessing it through their mobile device—up 12 percent from six months ago.