How do I find my missing Turtle in a backyard full of grass??

I was wondering if anyone could help.
During the day, I usually take my two baby turtles out to bask in the sun. I keep my eyes on them and usually have no problems. Last week, I took them out and turned my attention to my son for a few minutes; when I looked back I couldn't find one of them. It's been 6 days and I haven't been able to find her. I've looked everywhere:raked the grass, crawled on my knees and nothing.
Does anyone know how long a turtle can survive without food/water? I've been wetting the grass often, since it's been sunny and yesterday and today it's been raining.
Is there anything I can do or use to get her to come out of hiding?

I have hope that DanDan (that's the name my son gave it) is still alive. I look everyday in hope that I find her. She was the timid and shy one...she usually doesn't go far.
Please, if anyone can suggest anything I'd greatly appreciate it.
Yes, it's a red-eared slider

I have teo turtles and do this as well, I had this problem once too and was lucky enough to find them. Contrary to popular belief, turtles can actually move pretty fast and find ways to get out of fenced areas. DanDan is probably gone and may be dead if he ran into the road. May I suggest you purchase a small plastic pool (about $9 at walmart or petsmart) and place your turtles there when taken out to bask. good luck

First I thought maybe you could borrow an infra-red camera, if you could get your hands on one. If he didn't dig a hole, how about pulling a string taught between two people, and swiping it across the grass in rows. Perhaps it would catch the turtle as a bump. How about borrowing a police bloodhound? Sounds silly, but maybe you know someone.

Well was it a Red-Eared Slider? Or Boxer because boxers tend to dig holes under the ground. That's how mine got away. It dug a hole under the fence and ran away.

Can you get a good sniffing hound dog? My dog can sniff and find a bone he has buried and sometimes he can locate a lizard. I'm sure you have a neighbor that might have a dog
sniffer you can borrow!