Feed them anything?
What size containers?
How hot is hot ?
Did you try shaking the vines to release pollen ?

Hot and humid = flowers but no fruit set. The nighttime temps have to be at or below 75 degrees consistently for the flowers to pollinate. And high humidity makes it worse.

Thanks for getting back to me. Acutally they are planted in trenches in the floor of the greenhouse. i did try shaking the vines a couple weeks ago but still no set fruit. I did give them fish emulsion about a month ago. I don't have a themometer in the greenhouse (quess I will have to invest in one for next year)but I'm sure it is over 100 at times because it has been 85+ outside and inside it's worse. It appears I should vent more at night or maybe later afternoon it has been in the mid 30's at times and also need to vent to get rid of the humidity There is actually something mosslike on the ground in places I'm sure that is because of humidity because our area is generally low in humidity (lower mountains Montana) Thanks for your help - Any more suggestions out there??

It is too hot for them. Optimal temps are more like 80 during the day and 60 at night. Also they need air movement to cause pollination to happen when it is in the proper temperature range.
I'm wondering as to why you planted them in the greenhouse and not outside.
Remy

Thanks for the info. I planted them inside because it is not uncommon to have a frost in mid june and early august in fact one year I had a frost every month of the summer I guess i was thinking I could extend the growing season a little. looks like I will have to rethink how I grow using the greenhouse.

Give them a fan for air movement. Or shake their stakes once a day.

Have you thought of automatic temperature-activated vents?
http://www.harborfreight.com/greenhouse-window-vent-opener-92192.html
That was just the first I found in a search. Here are a bunch of different kinds (not all automatic):
http://www.charleysgreenhouse.com/index.cfm?page=_a2&cid1=842&cid2=200

Wow! Frost every month!! Now I understand : ) As long as you can control the temps better and get the air flow, you will be successful next year.
Another idea is of course pots with small determinates or dwarfs outside that can be easily moved into the greenhouse should cold night temps be approaching. With those types of tomatoes, the pots do not need to be large.
Here's a determinate cherry tomato in a pot.

Thanks for the help Looks like I'm going to start a shopping list for next year - max/min thermometer, small fan, automatic vent opener. After the disappointing year here (Did I mention the deer jumped the 6 foot fence and had a heyday?)I'm ready for some successes Thanks again.