Brother you have good ambitions but nothing comes up without any cost, i don not think any one will do free advertisement for you its a job for them for which they will not get paid, everyone catch up that point which gives themselves some return. so you need to invest in present to make your future.
giving it for free and only Op can benefit for a free service i think no professional can do that job for him. If you cant pay for that service then learn how to make your own way for advertisng than asking member here for free .
Well there are many ways now for advertisment you should only know how to do that.
That would be the result but there's no one will spend their time for nothing in return since all professionals and new start ups will ask payments for their efforts, since OP want his advertisment for free then he should be the one who do it since as you said there are so many ways and social media posting is a good platform to start with but this will be hard and take a lot of work + efforts but for sure this can get a low result.