Police in Lancashire are hunting a man from Chorley who posted "sick" comments about missing schoolgirl April Jones online.
His comments sparked an angry backlash on Facebook.
A vigilante group is reported to have called at the man's parents' house in Chorley.
Lancashire Police confirmed it was investigating the comments and was looking for a man in connection with their inquiry.
More top news
A murder investigation has started in Rochdale after a woman was found dead.
A man has been charged with the murder of an 80-year-old woman at her home on Merseyside.
Storm Brian moves away... mixed week in store, with warmer temperatures and some sunny spells