Police have released a photo of a suspect wanted after a woman was allegedly sexually assaulted in Millennium Park on Tuesday.

EMBED >More News Videos A woman was sexually assaulted in a stairwell at Millennium Park after chasing a man who snatched her cell phone.

CHICAGO (WLS) -- A woman was sexually assaulted after police said she chased a man who snatched her cell phone out of her hand.According to police, the 27-year-old woman had just gotten off a Red Line train near State and Lake and was walking past the Daley Plaza near Dearborn and Washington Tuesday at around 4 a.m. when an unknown man grabbed her cell phone and ran off.The victim chased the offender into the street and eventually down to the riverwalk into a secluded area according to police.When the victim caught up with the thief near Michigan and Randolph, the man allegedly forced the woman into a stairwell of the Millennium Park parking garage and sexually assaulted her before running off again.The victim was transported to Northwestern Memorial Hospital in stable condition.The attack has left many people that live and work in the Loop on edge."It's just a lot going on. It's scary, sometimes I get off work at 7 o'clock, so you just never know," said Stacey McCalister, who works in the Loop.Michael Edwards, the president and CEO of the Chicago Loop Alliance, which promotes the Downtown Business District, said he would love to see a larger police presence in the first district. In the interim, he said he would consider expanding the hours of the safety ambassadors and security guards his group already provides."If there's something we can do sort of in between to address issues and keep people safe and happy in the Loop that's what we want to do," Edwards said.The Chicago Loop Alliance said cellphones are a big target in the Loop. They said they believe cellphones are the number one reported theft in the Loop.Police said the alleged offender is described as a black man between 25 and 35 years old. He has long black dreads.He was wearing a red/black hat, black t-shirt, black pants, black shoes, and a dark/multi colored backpack, police said."Should have never happened. Should have never put his hands on her should have never took her stuff in the first place. Simply turn yourself in, your picture is out there," said Andrew Holmes, community activist.No one is in custody. Area Central detectives are investigating; if you have any information, please call them at (312) 747-8380.Police are also reminding people to be aware, especially when on your cell phones.