How do I spread the promotion?

In the past year we have gone from launching a VPN service to having almost 200,000 or so users and making a profit every month, but very little. (Because we have a very low promotional budget)
Because there are so many users who like our product, we want to expand our audience through marketing.
I would like to ask you how we can achieve a more efficient promotion? Do we need to find investors or increase the promotion budget?

website: http://surfshell.io/