As the founder of link removed, I'd like to say that there is actually a ton of freely available, scientifically reputable information on the subject - you'll just need to look around for it. The body of work in this space is growing, and to really learn about it you will need to take a little dive into the world of plant electrophysiology to learn about the search terms to find what you're looking for.
To start, I would point you to look at the collection of papers in the book edited by Volkov - I can't find my link so easily right now, but if you look up "plant electrophysiology" in google books, you'll find some free excerpts that will be of interest.
A reader of my newsletter just sent me the following link that describes some research out of Korea where scientists were stimulating lettuce & hot pepper plants with 2-10 volts and achieving gains in growth and pepper size. What's especially interesting to me is their use of DNA testing to look for genetic changes (presumably gene expression) in the soil & root bacterial populations as the plant grows, across both electrified and control groups: http://file.scirp.org/Html/2-3000235_19031.htm
While the formatting isn't that great, there were some experiments done by the Missouri Botanical Gardens in 1918 that show promising results from DC electrification: http://wwww.archive.org/stream/mobot31753002460860/mobot31753002460860_djvu.txt
If you were interested in seeing how AC fields are beneficial to tomato seedlings, you can check out this paper: http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.agro-3591e99e-32b2-4534-9733-fa6ab7bb9ab6/c/Patwardhan-403-413.pdf
Regarding magnetic stimulation, here's a paper I found but haven't read yet that you would find interesting (my focus for the time being is DC & pulsed DC forms of stimulation): http://www.actahort.org/members/showpdf?booknrarnr=399_15
Within my close circles, I and my fellow experimenters have personally experienced accelerated and increased growth of tomatoes, broccoli, radishes, sunflowers, squash, and corn.
I recommend starting off by doing some research - try to go a little bit deeper before dismissing what's possible. I believe that if you search around for awhile you'll come across people finding success with audio signals, ultrasonics, high voltage electric fields, and more. Best of luck!
