The aquarium trade transports countless ornamental species around the globe, creating greater opportunities for unwanted nonnative organisms to be released into the wild. The buy-sell-trade classified sections of print newspapers are a relic of the past. Instead, hobbyists now use social media platforms and Internet forums to create virtual communities where the acquisition of plants and animals via informal peer-to-peer transactions is possible. The present study aimed to investigate the behavior of aquarium hobbyists by administering a survey to Facebook groups in the U.S. that facilitate, among other things, the rehoming of aquatic organisms. In practice, “rehoming” actually refers to the selling, trading, or gifting of plants and animals, despite such activities being prohibited by Facebook’s commerce policies. According to 1,743 hobbyists, over half (54% of responses) of the respondents sometimes to very often engaged in peer-to-peer transactions (i.e., selling, trading, or gifting) using online platforms, with the most common motivator for owning unwanted organisms resulting from accidental or purposeful breeding (25.5%). Respondents reported local delivery or pickup of unwanted organisms in a different county (36.2% and 41.0%, respectively), state (13.9% and 29.1%), or country (6.2% and 5.6%). A total of 1.3% of hobbyists reported releasing live organisms into the wild, and over one-third (37.2%) claimed to have known someone who had done the same. Respondents who self-identified as releasing live organisms in the past (“releasers”, 2.9% of respondents) reported similar levels of invasive species knowledge, yet were over three times (15.7% of “releasers” vs. 5.3% of “non-releasers”) more likely to be unconcerned about their negative impacts, and over twice more likely to report feeling not responsible for helping prevent their spread compared to non-releasers (19.6% of “releasers” vs. 9.6% of “non-releasers”). Social media platforms, such as Facebook, offer extensive opportunities for peer-to-peer transactions involving live organisms. Outreach campaigns specifically targeting online hobbyists are necessary to discourage the intentional release of organisms into the wild, in addition to effective autonomous surveillance of discussion forums and enforcement of existing Facebook policies that prohibit the buying, selling, and trading of live animals.