The pets in Petula's posse are the primary antagonists of Littlest Pet Shop: A World of Our Own. The group consists of Petula Woolwright, who is unofficially the leader, Sweetie Pom Pom, Gavin Chamelle, and Mitchell Snailford.
They are essentially a group of bullies, as they parade through Paw-Tucket causing distress to other pets. They've done everything from simply discouraging and name-calling pets, to humiliation, to flat-out trickery and manipulation, pretending to be pets' friends only to turn on them later. None of them are above cheating in order to get their way.
Each of the pets in the posse has a softer side and their own insecurities, even if they rarely show it. In all likelihood, none of them are completely bad through-and-through.
For example, even though Petula invited herself over to Roxie's slumber party in The Big Sleep-Over, she didn't do so with the intention of ruining Roxie's night; She just really hates not being invited to parties, and all the pets at the slumber party ended up having a blast with her.
Seeing as bullies will be bullies, though, Petula's posse currently just aims to cause conflicts, and they aren't interested in making any friends. They enjoy getting a rise out of the pets in Paw-Tucket, not really caring whether or not other pets like them.