Feeling lonely

I have very few friends, and those I do have are often away doing their own things and dont have time to hang out. I'm quite introverted, but even when I do want to have a social interaction and do something with someone, there is often nobody replying to me. I feel completely isolated, as if nobody really liked me to begin with. I have tried making friends online, but I find it harder than real life for some reason. I volunteer on an old railway line, but most people there are middle aged to retired, and those around my age I see maybe once a month. All this is to say, I have tried. I'm guessing that theres at least a few people here who have been in a similar situation, anything I can do to deal with it?