Analyst: Advertisers cannot ignore Gen Xers

As it turns out, millennials are the ones doing the most online shopping but they're not the ones spending the most money. (Tweet This)

A new report by Comscore, on the digital habits of millennials, found that the 35- to 54-year-old segment, also known as Gen Xers, are spending the most money online.

So why are advertisers intensely focused on young spenders?

Gian Fulgoni, co-founder of Comscore, told CNBC's Squawk Alley it has to do with brand loyalty.

"It's believed that if you can establish loyalty to your brand early on in somebody's life, you have a better chance of then maintaining that brand loyalty as the person ages," he said.

Are millennials worse off than Gen Xers?

Fulgoni added that Comscore hasn't seen any evidence of millennials spending less time on Facebook. In fact, about an hour of their day is spent on the Facebook mobile app according to the report.

"In total they spend about four hours a day online," said Fulgoni. "So they're very, very heavy digital users and very heavy social users." This fact, something digital advertisers have to keep in mind.

Fulgoni said another aspect advertisers should factor in about millennials is how their digital habits differ from Gen Xers.

Gen X now more affluent than boomers: Survey
Gen X now more affluent than boomers: Survey

"[Millennials] are much, much heavier viewers of video and television content on these mobile devices and that's something that's of great concern to all the advertisers, coupled with a question about whether as they age, will their behavior patterns revert back, to some degree, to mimic that of older people."

Despite the challenge of catering to millennials, Fulgoni said marketers cannot afford to ignore the older, middle-aged segment because that's where the spending power lies.

In fact, Gen Xers' index of spending power is 25 percent higher than average, according to Fulgoni.

"You really have to spread your wings a little wider than maybe what ideally you like and that kind of increases the cost a little, I think, for any marketer," he said.