JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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It is always best to be able to set it all up in one location and have it cover as many different social networks as possible.
For that reason, I believe that this widget is the best match for what you are after: Social Share.
It will allow you to add the image, title and the link to a page to share, while in the same time offer you to share it on Facebook and on Twitter (it would of course not be able to share on both places in the exact same time, but both options would be available).
You can see here how to add the widget to your jotform: How to Add a Widget to your Form
Do let us know if you have any questions in regards to this and we would be happy to assist with them :)