Firstly, you don't need a co-founder but it's highly recommended, investors on the whole will trust a team of co-founders more than a single founder. The reason is that statistically co-founding teams are much more successful than single founder teams. Why bet on a company, even with a great idea, that has less chance of being successful.

Having said that you can find investors who will bet on you, it's just a case of kissing lots of frogs.

If you have an MVP, you need to use it to validate your assumptions. That does not mean that you need to get 100,000 users on board. You need enough users to show average usage. I'm not a statistician but depending on your customer base your sample of users could be 10 (B2B - enterprise) to 10k B2C mass market.

Proof points would be:

* stickiness - how often the come back and use it
* conversion to sales
* NPS - would they recommend the product / service to a friend?
* there will be lots of other specific qualitative and quantitate proofs that will be specific to your product

It should not take you long to put this together in a presentable form and take it to investors.

Happy to help you further on a call, including working out specific KPIs or proof points.