Can social media channels be used to submit FOI requests?

The Information Commissioner says they can, yes:

While Twitter is not the most effective channel for submitting or responding to freedom of information requests, this does not mean that requests sent using Twitter are necessarily invalid. They can be valid requests in freedom of information terms and authorities that have Twitter accounts should plan for the possibility of receiving them.

Similar principles apply to Facebook, and the ICO provides suggestions for responding via email (asking a tweeter to provide an email address by @reply or direct message) or by posting the information on your website and tweeting a reply linking to it.

for more examples and tips