Should I "as well as I" or "as well as me" in the following sentence?
John visited the party last night as well as I/as well as me.
Should I "as well as I" or "as well as me" in the following sentence?
John visited the party last night as well as I/as well as me.
Your question forms part of the long debate over the uses of the personal pronouns I and me. The issue arises partly because in most contexts usages such as: It is I tend to sound archaic and formal.
For example, the majority of English speakers would probably say: It's me at the door. rather than It is I at the door.
Most confusion occurs when speakers are not aware that I and we are used as the subject of the verb and me and us as the object, whether direct or indirect.
So one hears people saying things like: Me (or Myself) and my friend were at the party and This comes from my wife and I. These are simply wrong.
Coming to your particular question: while it's correct to say:John visited the party as well as I, it sounds all wrong and very few native English speakers would say that.
Nearly all would say as well as me in the same way that they would say It's me at the door. The use of I sounds more natural if you add did. He visited the party last night as well as I did.
Things get a bit trickier in constructions such as: It was I who gave them a lift. You are likely to hear: It was me who gave them a lift but this (me gave) is wrong - at least until such time as popular usage makes it inevitable.
So the short answer to your question is that if you want to sound natural, prefer me; or add did after I.
https://english.stackexchange.com/questions/96718/which-is-correct-i-or-me
http://www.learnersdictionary.com/qa/when-to-use-i-and-when-to-use-me
http://grammar.yourdictionary.com/style-and-usage/when-to-use-i-or-me-in-a-sentence.html
This situation is actually different from the often discussed examples like 'than I/than me' (https://english.stackexchange.com/questions/461930/what-should-come-as-object-i-or-me/461932#461932) where a choice is possible to use I as the second subject or me as an object. If the sense is that both visited that party, it's about subject and there must be I:
John as well as I visited the party last night.
With another word order (like in the question) you most likely need to 'refresh' the verb (as you can see, me did is impossible):
John visited the party last night as well as I did.
If you simply use me,
John visited the party last night as well as me.
the sense will change to 'he visited both the party and me' (me is an object).