There is no tranny drain plug built into the tranny or pan. At least not stock. I'm pretty sure the plug your talking about is just a rubber dust cover/plug for the bell housing. It doesn't hold oil in. The thing inside the whole is the torque converter. You can pick up a new plug at your local dealer or junk yard.
The dipstick doesn't go all the way to the bottom. So there may still be some fluid in the tranny. Just not enough to register on the dip stick. I wouldn't drive it until you've filled it back up.
It does, however, look like you've got a pretty bad oil leak somewhere. Can't tell if its engine oil or tranny oil though. Good luck...
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'98 3.8L Convertable (Red w/ White top)
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