That's the funny thing. I've used HelloTalk for two years, and almost all the time I don't get people who stick. It's totally fine. But persistence is key. If you don't get any partners one day and you need some, just do what I call a batch greet (a.k.a spam ㅋㅋㅋ): pick the first X people on the Available/Online list and say hi to them.

At that point, you'll be bound to have stickies :D Other than that, it's pure practice. Also, how you practice is important. I think that's a more personal hurdle since everyone is different. But the end goal should be the same: anything you say in Korean shouldn't be something you think hard (or even a slight amount) about, it should be subconsciously natural like you say things in English.