I'd suggest putting together a prototype at least, if feasible. Note that you needn't be an expert in C++ or the like to do this: there are various engines, frameworks, and languages that could make things easier. (And many of these are free, too!)
With a prototype in hand, you have something to show to potential investors (whether publishers or other types). That may well improve the likelihood of some or other party taking you up on funding.
If you haven't done so already, you may also want to look into putting together a pitch-document. My understanding is that these allow publishers to quickly get an idea of what you want to make, what's exciting about it, what your plans are, and who you are.
I've seen two sets of information regarding the making of pitch documents--let me link them here:
The first was posted by a publisher, and provides a template for the construction of a pitch deck:
Raw Fury pitch deck templateThe second is a sample of actual pitch decks, I believe, and thus provides examples for reference, in some cases along with notes.
Pitch Decks