http://lmgtfy.com/?q=root+tomato+stems

You can choose among several thousand posts.

You can also find many how-to posts over on the Growing Tomatoes forum here. Note that only certain parts of the plant can be used.

Growing tomato cuttings discussions

Dave

I had a few of the large lower "suckers" break off during a windy day a while back. I cut them off clean and just stuck them in a container with potting mix, kept this damp and all three are doing well now. I did it more to test it out than anything, it's too late for these to produce for me this year.

Zone 3a here. Just planted a bunch of tomato clones for a fall crop.

Take a branch and stick it in soil saturated with water. Anything just touching the soil will root

Is it a special variety that you want to preserve?