The sentence "Thank you all for your support so far" is correct and usable in written English. You can use it to express gratitude to a group for something they have done or experienced before. For example: "I would like to thank you all for your support so far on this project. I could not have done it without you!".
Thank you for your support so far.
And thanks for your support so far.
Thank you all for the support".
Thank you for all your support thus far and here's to the future!
Thank you everyone for your support".
Thank you for all the suggestions so far.
Thank you for your support.
Ludwig does not simply clarify my doubts with English writing, it enlightens my writing with new possibilities
Simone Ivan Conte
Software Engineer at Adobe, UK