Perhaps leafminers?

If so, they are between the top and bottom surfaces of the leaves. Squish 'em!

Hmm, those don't really look like leaf miner trails to me. I haven't seen patches like that before. Perhaps this link will help you identify the problem.
http://aggie-horticulture.tamu.edu/tomatoproblemsolver/index.html

leafminers are of two general types -- serpentine (with a narrow winding trail) and blotch (a larger spot).

If the blotches in the photo are blotches from leafminer, the critters have removed the tissue between the top and bottom layers of the leaf. Thus, it will be easy to separate the leaf layers at that place.

Try that easy test, then get back to us.