Check out the RoC filings to see if they have changed their address. If not, send a notice to the last known address, preferably the registered office address. The notice needs to be sent through registered post acknowledgement due. Even if the notice is returned, you can file a 138 complaint. However, continue tracking them down, cause, you’ll necessarily need to locate them in case you file a complaint and the Magistrate issues summons/warrants to the accused.