The head of the Philadelphia Housing Authority has gone missing. The staff and the board of the PHA have been unable to contact Carl R. Greene, executive director of the agency, since last week, after it was disclosed that Greene's bank had foreclosed on the mortgage on his $615,000 townhouse and that the IRS had placed a lien on the property because Greene owed the government $52,000 in back taxes. Greene paid of the IRS debt and the lien was lifted. He still owes thousands in back mortgage payments. Former Mayor John Street, chair of the PHA board, said he has been trying for several days to reach Greene via phone and email, but no luck.