Try a search for tomato plant cloning

Here is a link that might be useful: Google

Tomatoes are very easy to clone. Take about an 8 inch bud vase and make your cutting so it will go almost all the way down to the bottom of the vase and have a few inches above the vase. Trim off the leaves from the stem that will go in the vase and pinch off any flowers or buds. Put in a sunny window and keep the water level constant and you should get roots very soon. the more roots you let develop before you plant it out, the more likely it will survive outside. A friend at work clones his in wine bottles.

Other points on cloning:
1. Not all cuttings will root and some types of tomatoes seem to me to clone easier than others.
2. What diseases that the parent plant has will be transmitted to the clone, so at least start with as pretty a cutting as you can get.
3. "Suckers" root easier than main trunk cuttings IMO.
4. Clone more plants than you need to account for failed rootings and transplant fatalities.
5. It is usually better to start only one clone per vase or bottle so the roots don't have to be separated when it is time to transplant outside.
6. Clones can be ready to plant out in as little as a week and the sooner the leaves return to full sunlight the less likely they are to sun-scald.

If you have seed left over (so it's not a matter of wanting to save a particular variety), is it better to start seed early, or take cuttings late in the season and overwinter the clones? I'm thinking that if you have the room (and the proper conditions), a clone would be bigger at transplant time and *might* bear earlier than something started from seed 2-3 months before setting out. Not sure how big the clones would get over the winter - how large a pot (1 gal OK?), etc. And large plants don't always transplant well. But I'm willing to try a dozen or so to get a jump on the season.

All the previous discussions here on how to root cuttings.

Here is a link that might be useful: Rooting cuttings discussions

I will say yes if it is the very tip or a sucker off of an indeterminate plant. I did this last year, mid August (frost usually by mid September) and grew it indoors. It was spindly and pathetic, and stopped growth during December and January. February I saw new leaves off the top, let those grow, then pinched back to hopefully encourage a sucker or two from the branch axils lower down. I also rooted the tip. I took 4 cuttings from the plant this way, the tip, and then each subsequent sucker branch when they got to be 3 inches in length. The last 2 cuttings I took (near mid April) grew the best and were the ones I put out in the ground. They have grown like monsters with the exceptional heat we've rec'd this summer.

Reason I did this was because I liked the tomato (sunsugar cherry) and knew it was a hybrid, so saving seed was out. Plus, I was paranoid that all the local places wouldn't offer it next year, and I've wanted to try this experiment ever since I'd read about someone else doing it. This spring I made a mental note of the (2) places that did carry sunsugar cherry should I want it again (and one was sold out already when I asked about it), and I see that I can also buy seed for it. One thing that makes me nervous about this method is should the mother plant have some disease or genetic flaw, that of course, will be carried to next year's
crop. I had fun though, and enjoy eating those tomatoes knowing they are from 2011's plant!