Reporting people for evading taxes is good when there is legitimate evidence to back up such accusations. However, this #ThotAudit movement has simply gone too far. It has reached a point where it's being used to harass those who have done nothing wrong. Roosh V. is accusing Brittany Venti of tax evasion without any sort of legitimate evidence. The only "evidence" he gave, to summarize in my own words, was that "she locky her accounty hehehehe." Not only that, but he's encouraging his followers to report her to the IRS. This is pretty much the fiscal equivalent of swatting in the sense that it is people misusing the IRS reporting system in bad faith. And I honestly condemn anyone who is misusing the IRS or any other government system, service, or agency as a harassment tactic. Zero respect for those kinds of people.
I'm not knowledgeable here because I've never touched Instagram/snapchat/twitter, but my guess is that gifts are the issue. I'd hazard a guess some of these girls are getting pricey gifts from orbiting suitors suckers and not reporting them. Culturally women receive more gifts than men. Investigating only money donation platforms is not as big of an issue specifically when auditing an internet model.
A few things to note (about US law, anyway). First is that a cash gift is only taxable when in excess of $15,000 for the year. Stocks and real estate are treated the same way.
Second is that the donor is the one taxed for making such a gift in most cases.
Third: a gift is defined as a transfer where compensation is not received in return, and is generally characterized as "detached or disinterested." By this metric, it would not be hard for a donor to argue that something like a photo was the compensation (making the recipient responsible for paying income tax), and the recipient could just as easily argue that the photo was unrelated (making the donor responsible for paying a gift tax).
In regard to the third point, crowdfunding platform transactions are not considered gifts, as there is a promise of goods or services at some point. Funding through platforms like snapchat and other cam-whoring sites are not gifts either, since appearance on camera is considered a performance, and therefore a service rendered.
So in a sense you're right that gifts are the issue here for the IRS, but its the donors that are likely evading these taxes in most cases.
Tim Pool made a good point when he said that in his personal experience, platforms that collect revenue for him report this info to the IRS and the IRS has notified him in cases where he forgot to pay taxes on that income. So most of this is wasted effort, outside of a few edge cases where the girls in question handle their payments through a third party such as Paypal.