Police are alerting Boston-area residents, especially college students new to the area, to a series of attacks along the Charles River between 2007 and 2009 and the man police say is behind them.

The Massachusetts State Police held a press conference on Wednesday at the Hatch Shell on the Esplanade, the area along the Charles, to encourage people to stay vigilant.

Police released a computer-assisted rendering of the suspect behind a string of assaults against young women. Authorities said the victims described him as a black man of medium to large build in his mid-20s to mid-30s.

“We do not yet know who attacked these women, but we will pledge to you today to never stop in our efforts,” State Police Col. Marian J. McGovern said at the press conference, according to video posted online. “All we ask is that you be careful.”

On Thursday afternoon, the Harvard University Police Department issued a community advisory to alert students, especially freshmen, to the attacks.

Authorities believe the suspect is responsible for three attacks on the Esplanade in June 2007, July 2007, and July 2009. He may also be linked to an attack at Joe Moakley Park in July 2006.

“We don’t want you to panic, and we don’t want you to live in fear,’” said Suffolk District Attorney Daniel F. Conley at the press conference, according to online video. “We want you to enjoy this beautiful city, but we want you to do it safely and keep an eye out for your friends and fellow citizens.”

The police have added extra patrols, and both the Massachusetts State Police and Boston Police urge students, especially new students in the area, to practice extra precaution while walking or running along the Charles and in the city after nightfall.

—Staff writer Julia K. Nguyen can be reached at julianguyen@college.harvard.edu.