Kidnapped (1987)

Sisters Bonnie and Debbie visit San Diego on Debbie's sixteenth birthday. After telling a sleazy pickup artist to take a hike, he follows them to the zoo and has Debbie kidnapped on behalf of his sleazy boss in order to shoot her full of dope and make her perform in porno films. Despite admonitions from the abductors, Bonnie teams up with detective Vince McCarthy, and together they try to infiltrate the porno industry in order to rescue Debbie.