Estimated 18.6M Watch 'Joey' Debut on NBC NEW YORK - Based on its series premiere, Joey Tribbiani is missing a few viewers along with his "Friends." An estimated 18.6 million people watched the first episode of "Joey" Thursday, the spinoff of "Friends" that NBC was counting on to keep its Thursday night lineup strong, according to Nielsen Media Research.    That's lower than any original episode of Matt LeBlanc's old series drew last season, including the 24.5 million people who saw the season debut...