You have to go out a night with a flashlight, that will surely show up the pest, likely a slug or caterpillar such as a cutworm. Some noctuid moth caterpillars are active in a mild winter such as in California.

I did couple of times but couldn't find out and will continue to do the same. I noticed earwigs back in the garden time to time. Can they eat the entire plant? Posting another image but this is different. Will slug / caterpillar leave any trace?

The damage in your second image appears to be from caterpillars.

Have you looked closely on the undersides of the leaves? Some caterpillars are green And all are very small when recently hatched.

Slugs and caterpillars can eat the entire plant. And in a relative blink. Evidence of slugs include slime trails of course, and caterpillars leave frass particles, but that is not noticeable on dark soil, only seen on large foliage where it sticks to leaves.

This post was edited by larry_gene on Tue, Feb 11, 14 at 22:58

Do you happen to have any diatomaceous earth? If so, spread it around the base. For many garden pests, if they have to crawl through it, it will be their last time.

I do this with all my broccoli seedlings since I had an attack similar to what your pictures show a few years back and have had great success.

Best of luck!