The incident occurred at about 8:40 p.m. on August 26 in the 5500-block of North Sheridan Road.
Police said the intruder came into the lobby and battered the doorman. He continued into the building and then walked out a short time later.
Police said the man was wearing a black baseball cap, blue T-shirt and black pants.
Anyone with information is asked to contact Area 3 Detective Hendry #20218 at 312-744-8263. Anonymous tips can also be sent to www.cpdtip.com. Police warn if you see the suspect, do not approach him and call 911.