https://arstechnica.com/information-technology/2012/06/reddi...
..and it turns out it's right on Reddit's wikipedia page as well:
> Supported by the funding from Y Combinator,[28] Huffman coded the site in Common Lisp[29] and together with Ohanian launched Reddit in June 2005.[30][31] Embarrassed by an empty-looking site, the founders created hundreds of fake users for their posts to make it look more populated,[32] an example of a fake it till you make it strategy.
Nobody would accuse a waitress of fraud for seeding the tip jar with a few dollars.
Now, if Reddit is doing fake posts in mass to change the valuation of an IPO, that would be the definition of fraud, specifically a public fraud the SEC could investigate. Reddit doing this at the start at best would be a civil investigation by any investors it had at that time, but it's highly unlikely any investors it had when committing said fraud would bring said investigation because it increased the value of its investment.