A former member of the legendary singing group the Platters has been missing for four days after getting a subway in Brooklyn, according to cops and her family, who warn that she has dementia and could be confused. Sandra Hall, 80, went missing around 4 p.m. Friday after boarding a subway at Atlantic Avenue near the Barclays Center and Atlantic Terminal Mall, according to the NYPD and her family. “Sandra is more than just our mother; she is a warm, vibrant woman who once brought joy to audiences as part of the Platters,” said her daughter, Star DaSilva. “We just...