ABC Family has given a fourth season to hit drama “Pretty Little Liars.”“Liars,” the cabler’s No. 1 series of all time, topped in key young-adult and young-femme demos during its run this summer. Skein ranked as the top scripted basic cable series in women 18-34 and the top series in female teens. ABC Family has ordred 24 one-hour episodes, which will bow in the middle of next year. A Halloween spesh will air Oct. 23 as a part of ABC Family’s “13 Nights of Halloween” programming event, and “Liars” will return to complete its third season in January. “Pretty Little Liars” is produced by Alloy Entertainment in association with Warner Horizon TV. Skein is exec produced by I. Marlene King, Oliver Goldstick, Joseph Dougherty and Leslie Morgenstein.