Re: People Picker in alfresco 5.2 shows no results found, But can able to locate user from Admin Tools->Users ->User Search option
Agree with Angel, this looks like it is solr related. You should verify that solr is working correctly for other aspects of your system (like full-text search), and, if not, resolve that issue. You can try clearing your your solr model directory. Worst case would be a full reindex, but clearing out the model directory might do it.