On a similar note to likeatonneofbrick's post, maybe you aren't coming across as passionate, or coming across as too dispassionate.
One of my female friends recently told me that she was frustrated that whenever she was out with male friends, colleagues or whatever, none of them were ever remotely flirty with her. They'd joke and laugh with her, and talk the usual banter but none of them, whether she fancied them or not, would ever make so much as a suggestive remark.
I gave the matter some thought and realised that, even if I wasn't married, I don't think I'd consider even asking her out. And then it occurred to me that I'd never even thought about what dating her would be like. She has a nice face, she's clever, and she has a good figure, she's funny and pleasant. But she comes across as totally unsexual.
I don't know how she would change that - indeed, I chickened out of telling her. It's probably too late for the men who know her, but if she came across a bit more sensually next time she meets a man, he might flirt with her. But anyway, possibly you aren't seeming passionate enough.
Did you get as far as dates when you tried the internet? If so, do you have any idea why they didn't get as far as a relationship?
I suspect that once you are in a relationship, the next one will be much easier, as the pressure bubble will have burst, you will have more confidence, fewer nerves, and some experience of what being in a relationship is, like an expensive Premiership striker who can't hit a barn door at first but soon starts banging them in.