Generations of demigod and semi-demigod have been hiding and living among us to this present day, they made a pact with the god to never reveal the existence of God or themselves in public unless they yearn for early Armageddon. Most demigod and semi-demigod will eventually lose all of their power at puberty unless they can help it, in order to prevent losing their divine power they must have at least 1000 worshippers and 4000kg of unique and perishable offerings in last 365 days and their average puberty starts at age 12. My question is in this day and age how can the demigod prevent losing their power at puberty while keeping the wrath of God at bay?
Social-media for followers is just too obvious, so I'll concentrate on something else.
As a child, cultivate an interest in the Guinness Book of Records, now Guinness World Records. There are many achievable records with determination and practice - a chap whom I was once acquainted with got the record (as an adult) for running a marathon backwards for example. Such records as a child would have their own category which might even be novel.
To hide their identity, the help of the local cub-scouts (or equivalent) can be enlisted so that the individual is able to disappear into the crowd to a certain extent.
Selection of a suitable record should be accompanied by training, and with the stated purpose of raising money for charity a certain amount of publicity. If a splash of "overcoming adversity" can be added such as doing it after recovering from a broken leg or serious disease or condition (maybe faked - few media outlets seem to bother checking their facts much nowadays) then the publicity and charity contributions can be magnified (the media lap-up that sort of thing). When asked what the future contains after the record attempt - the godling should emphasize charity work, the poor and needy, perhaps even slip-in a mention to food-banks.
The aim for the setting of the record should be in the twelfth year, if the onset of powers occurs, then all the better to ensure that the record gets beat.
If not, then heat-exhaustion and collapse can become the headline - a valiant attempt. The record then can be re-attempted in a "comeback" after that setback with even more public sympathy and sponsorship. Then the powers might kick-in for sure. (Else, if puberty and transformation is very late then let's hope the training was enough).
Now a hero/heroine of the local community, a food-bank (with words in the ears of the right community-leaders) can be named after the budding deity. 4 tons per annum of perishable donations should be a doddle and the community will follow the website with the adolescent iconically spearheading the war against hunger. Job done.
To expand the idea, then further records can be attempted over time increasing the profile and spreading the initiative to further communities, perhaps even nationally - the god of "plenty for all" is born into the national consciousness.
start a cult
Ok so you are basically a child at this point. That sucks for trying to start this, and it's unlikely anyone but a very smart child would think about this, but there is a workaround. If you could enlist the help of a sympathetic demigod who has already met this requirement and is an adult by now, it would make things easier going forward, and you pretty much need one other person for this to start. Not sure how you plan on finding one, or getting one to help, or if that technically counts as revealing yourself, I'm going to assume it's been done already, and isn't an issue anymore. You are basically going to be the god they worship, without revealing yourself.
Get your friend to get a bunch of people to go to your place of worship, likely your basement or a field or something at the start because this is going to be a cult of a few people. Now your friend preaches about this new hip god called (demigod character). They may not believe it at first, but with you in the shadows, presumably using a camera to see what's going on, perform some miracles. Make sure they don't see or notice you, and hope that whatever this character's divine ability is, that it can work across some distance or without line of sight. Your new cultists see this, can't find any special effects tricks or wires or anything, believe it, and in turn believe you, and a few may convince their friends to come.
Congratulations; new followers. Once your cult grows faster and faster, then start collecting offerings and conducting rituals. 1000 people in a world of billions isn't that much. It doesn't reveal the existence of God, because you aren't a god but you're being worshipped like one. You never reveal yourself. And could be done rather quickly, a year or two of working your divine miracles from the shadows and boom, permanent powers.
EDIT: It might be revealing the existence of God if you conduct completely unexplainable miracles. But that's the thing. They are completely unexplainable. Is it God? who knows. Is it just really clever and well-done practical effects? maybe. You can't prove its actually magical or divine or anything.