According to Wiktionary, the only conjugation I can match this to is the conjunctive form, but that doesn't make any sense, given the context (as in "Help me!"). What would the equivalent conjugation of other verbs be here?
(Note: my background is perhaps equivalent to 1/2-year's worth of Japanese, gleaned through osmosis via animes and some books.)
Conjunctive form is just a label. It tells you about one of the most common uses of the -te form, but it's not a complete definition. Let's take a look at the relevant sense in 大辞林, a Japanese dictionary:
命令・依頼を表す。「てよ」「てね」の形をとることもある。
Translated, this says that it expresses a command or request, and that it can also take the forms てよ and てね. (In other words, this use of the -te form sometimes has the particles よ or ね after it.)
How does this make sense? Well, I was taught that this comes from either 〜てくれ or more politely 〜てください, with the くれ or ください omitted. So in this case, I think 助けて is a bit of a softer than the actual imperative form 助けろ.
「よ」、「ね」をつけて意を軽くすることもある.