Depends what the cause of the limpness is, have you kept them well watered? are they under cover or outside? A photo added to the question would be useful.

There are many reasons why this could happen. Trying to guess is futile. As Mg mentioned, a photo would help, but we'll still need an accurate history record. Wilting is a response to some action that you or somebody did or didn't do.

If underwatering is not the reason, I wonder if something has eaten the roots, like vine weevil etc ...

That's a possibility Hywel let's see what John has to say...

There's something called Verticillium Wilt which affects tomatoes, perhaps you could look it up.