Is it permissible for a supervisor of an Islamic page to reply to comments from young people with simple phrases such as: "And to you as well" or "O Lord"?

There is no harm in supplicating for someone who has supplicated for you, as long as you do not fear temptation, while adhering to the Islamic guidelines. However, it is better to avoid responding to them and to supplicate for them in their absence, for safety is paramount, warding off harm takes precedence over gaining benefit, blocking means [to evil] is a شرعي (religiously مطلوب (required) principle, and the temptation of women is among the greatest temptations. The Prophet, peace and blessings be upon him, warned against it by saying: "I have not left behind me a temptation more harmful to men than women," and "Beware of the world and beware of women, for the first temptation of the Children of Israel was concerning women."