This article introduces the use of Internet-mediated joint construction (JC) to engage second language (L2) writers to participate in virtual classroom activities in an online teaching environment. Affected by the ongoing COVID-19 pandemic, schools and universities in the People's Republic of China were required to rapidly transit to remote teaching. The switch from the traditional classroom-based scenarios to the online environment was challenging for teachers. One of the extreme difficulties is to engage students in virtual-class activities. To address this issue, the authors designed an Internet-mediated JC teaching practice and implemented it on ClassIn, an online teaching platform for one semester. Analysis of students' after-class online surveys and interviews suggested that the Internet-mediated JC practice helped students to build a connected network and thus engaged them in actively interacting with both the teacher and peers in the online environment. Pedagogical implications are discussed to contribute to the teaching practice of L2 online writing instruction.