By A. Ananthalakshmi KUALA LUMPUR (Reuters) - Digitally savvy Malaysian police have been taking to social media to issue warnings to critics of scandal-hit Prime Minister Najib Razak in an unusual online campaign that critics say is unlikely to work. Najib is facing the biggest political crisis in his seven-year premiership over a multi-billion dollar scandal at state fund 1Malaysia Development Berhad (1MDB) and over deposits of $681 million in his private bank account. Najib, chairman of the 1MDB advisory board, has denied any wrongdoing and says he did not take any money for personal gain.