In the episode A Knight of Shadows from the Justice League (2001) animated series, the Justice League and Etrigan were trying to find Morgaine Le Fay, to prevent her from finding a powerful magical object she was looking for.
Around the middle of the episode, J'onn suggests that he could try to locate her telepathically, before doing so. But Morgaine finds out.
Morgaine: Someone is reaching out to my mind, attempting to find me.
Mordred (smiling enthusiastically): Is it... him... ?
Morgaine: No. A mere amateur. He has no idea who he's dealing with.
Her son Mordred was thinking about someone. But who?
It didn't sound like it could be Jason Blood nor Etrigan. If they were able to use telepathy, they wouldn't wait for J'onn to do it (nor would they let him try, considering the consequences of attempting such a deed against a sorceress such as Morgaine).