Maybe a balanced or even a high nitrogen feed if they are young?  I steer clear of tomato feed until  the plants are much bigger and fruiting.  My young plants don't complain about the odd seaweed and urine cocktail!

I try and give all plants I raise a weekly seaweed feed (if I remember) from about 4-6 weeks after sowing until they get planted out. Especially with the recent compost situation I think this is even more important than previously.

I'm half out as of 10 minutes ago.  It's forecast to drop down to 7 here next week so no doubt they will go purple and sulk for 2 weeks while the ones I've held back race ahead.  Rest are out on Wednesday unless the forecast worsens.

It seems to happen when there have been big differences between night and day-time temperatures, I've found, and things seem to sort themselves out eventually.
Mine also suffered really badly last year, during the hot spell, but fruited as normal, and then when the heatwave ended they returned to normal..
Good luck with yours!

I push gently with a pencil and squeeze them a bit, then hope for the best.   Mrs Bouquet

Thanks both, I was planning to feed once I had put them out but I have given them a drink of tomato feed and will see if that perks them up.