Informed Consent Research Question I am a member of a closed, fairly large private group on Facebook of former game show contestants.  Several years ago, another member posted a Google Forms version of the Asperger Quotient test, asking group members to take the test, to report their overall score (anonymous), and to answer a few demographic questions on the form.  After collecting about 300 responses, he shared the composite results with the group (who were enthusiastic about the idea).  

I've since asked the member who composed the original post if he would be interested in turning this idea into a publishable research brief. I am a psychologist and faculty at a small university and could create the IRB/ submission at my institution.  My issue, though, involves about informed consent. The data is collected, but he did not include an informed consent statement with his Facebook post.  Should I scrap his data, create an informed consent, and then re-send out the AQ?  Or do you think I should submit a request to the IRB asking to use the existing data? 
Thanks!
I'd recommend consulting informally with IRB staff at your institution beforehand, usually (and maybe especially at a smaller institution?) they are willing to help out a bit at the design stage. Once you find the right person to contact, I'd convey to them almost exactly what you've posted here (probably via email), plus a bit more background on the actual current form of the data.

IRBs can vary quite a bit on what they allow; there are minimum standards they are required to follow but I've seen IRBs go well beyond those standards at times. It may be that the IRB decides the data are anonymous enough and low risk enough that you don't even need consent; it may be that they won't allow it in any form unless you start from scratch (and contacting the people who originally participated may similarly not be allowed; you might be able to solicit the group but not the previous responders directly).

There is likely a blanket prohibition on you collecting data, then trying to go back and get consent to use it in another way, but your situation is a bit different in that you weren't the one collecting in the first place and the collection does not seem to meet the criteria for "research" at the time of collection.

These flow charts from HHS might help a bit if you are in the US. Following Chart 2 and then Chart 4/5, it is quite possible that this work could be exempt from full review (but at least at my institution, it is still the IRB that decides whether the exemption applies).