The latest Comscore US social networking numbers are in for February, and here’s how Facebook, MySpace, and Twitter are stacking up.

Note: While these numbers may appear like growth has significantly slowed since previous months, Comscore does not normalize for the number of days in the month – February was 3 days shorter than January.

Facebook was basically flat for February at 57.4 million uniques (up 77% from a year ago), while MySpace fell 7% to 70.3 million uniques (up 3% from a year ago). If February weren’t 3 days shorter than January, uniques for all sites measured would have been about 10% higher.

At the same time, however, Twitter grew by an astounding 55% in February from 2.6 million to 4.0 million US uniques. The service continues to explode and was the fastest growing site by a longshot, according to Comscore.

Source: Comscore

Facebook’s recent comments that it is planning on opening up the service more and more may accelerate Facebook’s growth in the coming weeks and months. Facebook crossed 175 million global active users last month, and should be crossing 200 million active worldwide members very shortly.