Firstly, you would usually say "I just wanted to see how you 'were' doing." No, this doesn't imply that the person being questioned is going through a hard time, although they could be. I would say that this statement is fairly neutral - it's about updating yourself about somebody else's health/ feelings/ well-being/ status/ progress/ etc....

I think your sentence is perfect and appropriate. It does not imply that you are unduly worried. It might imply that you are a little bit concerned, but in a good way. One should always be concerned about friends. That's what friends are for. Here are some other ways to say the same: "u ok?" (suitable for a text message only) "I'm just checking in on you because I haven't heard from you for a while. What have you been up to?" (or you can use slang and say "whatcha up to?" or "what's up?" or "how's tricks?") "How are you doing? Just checking in." "Long time, no see. How are you?" "Any news? I've been thinking about you."

It's a neutral question it doesn't imply anything other than your enquiry as to how they are.

In this situation ( informal ) to be 100 % neutral, I would say ' hey, how are things going there?' and then you could go on to say something about yourself or suggest a chat or meeting or whatever you wanted to :)

hello can we practice together?