Despite a whopping 117% year-over-year growth in unique audience, which numbered 19.2 million in August, Facebook remained behind MySpace, which remains entrenched at the top of the US Social-Networking hierarchy with 60.3 million unique visitors, according to Nielsen/NetRatings.

The firm released data this week on August’s top US social networking sites, blogs and video sites, ranked by unique audience.

MySpace’s 23% growth in unique audience from August ‘06 to August ‘07 translates into an increase of more than 11 million unique visitors - or more than half of Facebook’s unique audience.

In short, in terms of absolute numbers, both social-networking sites gained similar numbers of unique visitors over the previous year - albeit one (Facebook) from a much smaller base, therefore all the more impressive.

Blog Sites 

Google’s Blogger remained atop the top 10 list of blog/host sites with 31.3 million unique visitors in August - 58% more than a year earlier. It was followed by AOL’s tmz.com, with 9.5 million.

The biggest surge in the blog category has been by WordPress, which had a unique audience of 8.9 million in August - or 322% more than a year earlier.

Video Sites 

Yet another Google property, YouTube, led the list of top 10 video sites in August with 56.5 million unique visitors - up 66% from August ‘06. Google Video, with 14.5 million unique visitors was third.

The largest growth among the video sites came from Veoh, which increased its unique audience nearly 350%, to nearly 3 million.

Sandwiched between the Google sites was MySpace Video with 16.8 million unique visitors in August - down 6% from a year earlier.

Yahoo Video, meanwhile, soared 101% from a year earlier, and is challenging rival MSN Video for the fifth spot.