Dong Dong Xu, a close friend of the victim, described Lin as timid and reserved, and often in the company of his boyfriend Lin Feng, who testified before the court last week.
Lin Feng told the court the two had broken up in the weeks before Lin's death, but remained friends.
Xu told the court he received a call from Lin Feng, who was vacationing in China, on May 27, 2012, asking him to investigate because Jun Lin had been out of contact for "more than 60 hours."
Xu, 31, testified he went to Lin's apartment, where he found a lone hungry cat and an oily frying pan with eggs on the counter.
After not finding his friend at the home, Xu tried Lin's workplace, a convenience store in Montreal's Verdun neighbourhood. He told the court he discovered that Lin had not shown up for work for two days.
Xu testified he was afraid "something unpleasant had happened" and went immediately to inform police, who asked him to inquire with the university.
Xu will continue his testimony Tuesday afternoon.
Magnotta has pleaded not guilty to five charges, including first-degree murder. However, he has agreed to the facts of the case, including that he killed Lin.
His lawyer told the court in his opening statement that he intends to prove that his client was not criminally responsible for his actions because of mental illness. He told the court Magnotta suffers from schizophrenia.
The Crown prosecutor in the case told the court he will present evidence that shows Magnotta had documented a plan to kill someone six months before Lin's death.