I've spent a fair bit of time in Greece in the last few years. My advice would be to fly to Athens and then let serendipity take over. It may well be that your friend heads for Piraeus or Raffina and a ferry, or gets a flight to one of the islands (probably just over an hour is the maximum flight time to any of them). Or maybe a hire car on the mainland - head for the Pelion peninsula, via the Parnassus.

Best hint - go with the flow, let the adventure happen, don't rule anything out and get involved rather than beng an onlooker.

PM me by all means.