A teenager is accused of robbing a Bucks County convenience store last weekend. 19-year-old Sean Foley of Southampton is charged with robbery and other offenses in a Saturday night holdup at the 7-11 on East Street Road in Warminster.  Police say he entered the store shortly before 7:30, indicated he had a gun and escaped on foot with an undisclosed amount of cash.  He was arrested Wednesday after police received an anonymous tip.