Breadcrumbing
Breadcrumbing is doling out small signs of interest — a message, a like, an occasional "hey, how are you" — without any intention of turning it into an actual date or relationship. The name refers to the crumbs used to lead someone along without ever feeding them.
The goal is usually to keep the other person's attention "just in case," even without real interest. Messages arrive irregularly and never lead to an actual plan.