One common way to express this idea is "seguir + gerund." "Es difícil aprender el español pero sigo intentando." (It's hard to learn Spanish but I am still trying.) "Ha comenzado la clase pero los estudiantes siguen hablando." (The class has begun but the students are still talking.) This corresponds well to the English construction "to keep (doing something)."

The best one is "todavía estoy intentando.." Todavía is important because it gives you the idea that you haven't achieved your goal yet. For example: I'm still trying to get a new job= todavía estoy intentando conseguir un nuevo trabajo If you remove "todavía" from the sentence it means that you are trying but not the you've already tried before. I'm waiting for him=Estoy esperándolo I'm still waiting for him=todavía estoy esperándolo Todavía coveys the meaning that you've been waiting for a long time and maybe some sort of complaint, as it does "still"in English I suppose.

Yo Todavía estoy intentando= I'm still trying

"Aún estoy intentando" or "Todavía estoy intentando". Regards!

I absolutely agree with the answer from Sebastiano... "Todavía lo estoy intentando" But Bryan is right... "Lo sigo intentando" is another good way to express it