Please don't be hateful.
Begging online usually starts with a sob story on something like Gofundme then you advertise your site on social media hoping people will go look and be willing to give money to you.
I looked at one today for a family with 3 kids who lost the house to fire so are living with family 2 dogs died and 3 cats missing only have the pajamas they were wearing. Another looked at lately was a woman who had cancer and only works part time who had the wheel fall off her van so has to spend hours to get to her part time job by bus.
So try to convince people you are more worthy of charity than these people, why we should give you money rather than someone like your mom who is raising you without her husband. The lady with the van got zero in 16 days. People are getting tired of people begging instead of doing for themselves.
Probably can't do it legally when under 18, needing stuff to make you happy is not a cause worth contributing, mom having cancer surgery may be another story.
GoFundMe.com is an example of a personal funding site, you might read through the various stories, again they would require you to be 18 to use the service.
At 16 you are old enough to get a job. Forget looking for handouts.
It's called crowdfunding, sites like gofundme.com and many others (google crowdfunding).
If you need life sustaining help, there are people willing to help, if you just want to buy something, you are out of luck.
sit on the corner with a sign. everybody else is