The key to a good friendship is how you start.
It is almost like making friends in your school or in business. 

This sounds mean and a little manipulative, but you have to be interested in them until they are interested in you.  Don't make a conversation about yourself until they ask you to. 

Example: 

You: "What are you doing?"

Person: "I am petting me dog." 

You: "Cool! What kind of dog do you have?"

Person: "I have a pug. He is lazy."

You:" I heard that pugs are bred to just sit on your lap all day and sleep."

Person: "That sounds like my pug. :P Do you have a dog?"  (They asked you. Now you can talk about yourself.)

You: "I do not have a dog. I want to get one. How did you prepare for your dog?" (Switch back to them. Most people like to talk about themselves so the person you are talking to will usually talk a lot. After talking a lot, they will feel that the conversation is very friendly.)

If you are interested in the person's life, they will be interested in yours. The person you are talking to will also think that you are very nice.
You can build a more comfortable conversation by asking them questions first. 

you can try again, don’t give up ...

How do you build a strong friendship normally? If you answer that to yourself, you may find out why it doesn't work that well for you online. And I'm serious, it's just not meant to be an empty phrase. For example, I doubt you normally build friendships by actually trying to build them, having to find things to say, manipulating people or expecting you can be friends with everyone. My personal take on this would be that it sort of happens by sharing your personal experiences and that's why it's much harder to do online.