Shares of Philip Morris International (NYSE: PM) plunged 16% on April 19, after the tobacco giant posted a mixed first quarter. That miss rattled the entire tobacco sector and dragged down Altria (NYSE: MO), British American Tobacco (NYSE: BTI), and Imperial Brands (NASDAQOTH: IMBBY).Some of the industrywide sell-off was justified, since PMI is the second largest publicly traded tobacco company and a bellwether stock.