Can you direct me to a specific website or place to participate in da'wah (inviting to Islam), and what is your opinion on online marriage sites?

Islamic websites concerned with Da‘wah (proselytizing) and disseminating Islamic knowledge are numerous, and one can cooperate with those in charge of any website known to be upon the methodology of Ahl as-Sunnah wal-Jama‘ah in matters of Da‘wah. As for online marriage websites, details concerning them have been previously elaborated upon in Fatwas numbered: 33749, None, and 98383.