To look around a place secretly, in order to discover things or find out information about someone or something. (Cambridge Dictionary)
To try to find out about other people’s private lives. (Cambridge Dictionary)
If someone snoops around a place, they secretly look around it in order to find out things. (Collins Dictionary)
Investigate or look around furtively in an attempt to find out something, especially information about someone’s private affairs. (Oxford Dictionaries)
To look or pry especially in a sneaking or meddlesome manner. (Merriam – Webster)
Social Media Snooping.
15 Relationship Experts Explain Why Snooping Is A Terrible Idea.