I do see only the installed core theme but community themes are not visible (count 0) and I am not able to search either. The packages manager is working, but the themes are not (I am using windows 10)
Which version of Atom are you using? Are you using the Install tab when trying to install themes?
After you go to the install tab, are you selecting Themes for searching?
My bad, working like charm, thank you for the help