Sorry for taking so long to see this. With the "Sentences" tab still missing (it's been over a month), we can't see any of the recent sentences' comments. :/
Βοηθείς is not wrong, but it's a bit archaic, literary. This is how the ancient Greek verb was conjugated in 2nd singular. It's been added, but I'd like to suggest that you use βοηθάς instead of βοηθείς. It's way more common, both in written and in spoken. ^.^
These verbs belong in the same conjugation category in modern Greek.
βοηθάω - βοηθώ
αγαπάω - αγαπώ
τραγουδάω - τραγουδώ
Be careful though. There is no such thing like αγαπείς or τραγουδείς. The correct forms are αγαπάς and τραγουδάς. Βοηθείς is still accepted for some reason but you should stick with βοηθάς. It's a bit more proper. ^.^
βοηθείς is also approved at. http://www.verbix.com/webverbix/go.php?D1=207&H1=301&T1=βοηθώ.