Other games "unlock" the next level if there are no friends to help so why don't you do it for Pet Rescue? My friends have all finished playing this game and I have no way of advancing so I will have to delete the game.
If you're enjoying the game then purchase some gold bars, it's only 9 to get to the next episode. It's the only way you're gonna be able to continue if you have no-one playing the game to help you out.