I understand their frustration, but it is wise to stop searching after dark. It's much easier to make a mistake without light.
It has been 6 days since he was last seen. It's probable that they are looking for a body, or he is in the ocean. He had 2 cell phones with him and it's important to note that he did not use either of them. If he had notice that something was wrong, he would have reached out. He did not. That suggests that something happened too fast for him to use a cell phone.
Greek SAR were provided with his location, as it was known to friends/family, and spent 2 hours searching by helicopter. They found nothing. They probably know the outcome of situations like this better than anyone.
As for the USA SAR, there is no crime and it is possible that he chose to disappear. That's how it is with adults.
The only time I've heard of a massive search for a missing woman from the USA was Natalie Holloway. Aruba gave everyone on the Island a day off work, the Dutch sent F16s with infrared to look for a body. It made no difference.
"Leshane said she was shocked at the bare-minimum efforts local authorities have made to find Calibet. She said they flew a helicopter in the area for just two hours the day after he went missing.
...
Leshane and Calibet’s friends have been starting their searches every day at 5 a.m., and they end late at night with strategizing their next search and rescue hike.
But, she said Greek authorities don’t seem to work past sundown."
same link
