TECHNICK

Just how big are MySpace and Facebook? Big enough to account for nearly 1 in 5 of the display ads Web marketers buy in the U.S.

That factoid comes via Web tracking service ComScore (SCOR), which says the two sites accounted for 17.4% of the display ads in the U.S. market in July.

News Corp.’s (NWS) MySpace, in the midst of a turnaround effort,  has a slight lead on Facebook  — 9.2% of the market versus 8.2%. That makes sense, since MySpace has always been aggressive about loading  up with ads, while Facebook has been fairly reticent, much to the dismay of the “when are you going to monetize?” crowd. (Click chart to enlarge)

That’s something you knew intuitively, of course. But interesting to see it in chart form.

Another data point you already knew, but may still find worthwhile to see in black and white — just how small the scraps are for the rest of much of the social network ad world. By Comscore’s count, the next 8-biggest social networks command a collective 1.4% of the market. (By the way, ever heard of MocoSpace.com before? Do you know anyone who claims to be a user?)

Remember that we’re just talking about overall impressions, not dollars. And ad impressions on social networks are famously cheap, so this stat only tells you part of the story. But it’s an important part. It illustrates the potential that the services have, even if they haven’t capitalized on it (not that they haven’t tried).

Meanwhile, here’s a bonus chart from Comscore, laying out the top advertisers on social networks. No surprise to see the likes of AT&T (T) and Sprint (S) there. But perhaps it’s noteworthy that Verizon (VZ) , the strongest US telco, spends the least on social media impressions. Meanwhile, social network app-makers/services like Zynga are spending heavily.

(News Corp. owns Dow Jones, which owns this Web site.)