When she started receiving unsolicited messages of a sexual nature from a male colleague, she ignored them initially.

But Tina (not her real name) reported him to her manager when he continued to harass her, only to be told she was overreacting. The manager refused to take any action, so Tina resigned as she felt unsafe.

Cases involving unwanted and explicit sexual messages and calls quadrupled between 2016 and last year, the Association of Women for Action and Research (Aware) told The New Paper on Wednesday.

The number of cases in which the perpetrator was from the victim's workplace also more than tripled in the same period.

This is consistent with a continued spike in technology-enabled sexual violence that the women's rights group has observed over the last four years. Its Sexual Assault Care Centre handled 140 such cases last year, triple the 47 in 2016.

The cases involved acts such as voyeurism and coercive sex-based communications enabled by digital technologies like social media and messaging platforms.

Aware's head of advocacy and research Shailey Hingorani said: "The terms surrounding technology-facilitated sexual violence - from 'upskirting' to 'SG Nasi Lemak' - have become depressingly common parlance in Singapore of late."

There were 41 cases involving unwanted and explicit sexual messages and calls last year. A third of the cases were perpetrated by someone from the victim's workplace.

Ms Hingorani told TNP: "We must bear in mind that sexual abuse cases tend to be severely underreported.

"In the case of workplace sexual harassment, many victims do not report the abuse because they fear they are not going to be believed or they are afraid of retaliation."

In some cases, victims do not know who to report to, or may not have faith that the management or human resource department will take their complaints seriously.

Said Ms Hingorani: "We recommend the introduction of workplace sexual harassment legislation that places legal obligations on employers to take active steps to prevent harassment and to thoroughly investigate every reported case."

Technology can also facilitate offline abuse, including rape and sexual assault. This happened in 50 of the 140 cases last year. For instance, ride-hailing or dating apps provide a platform for perpetrators to be connected to victims, said Aware.

In one case, a woman was raped by a man she met through a dating app. In another, a woman who hailed a ride to work was harassed by her driver who made explicit remarks, including how he liked to touch females on the train.

Both Grab and Gojek said they have zero tolerance for drivers and customers found to have such behaviour, and have leveraged technology to safeguard passengers.

Gojek Singapore general manager Lien Choong Luen said users guilty of harassment will be banned from the platform and reported to the police. He said the company continues to invest in prevention and other safety measures.

Manual verification of users is key for matchmaking company Lunch Actually, which has a dating app.

Chief executive Violet Lim said: "We have encountered very few cases (of sexual violence) in the last 16 years... Any action that causes harm or distress will be investigated thoroughly."

Image-based sexual abuse, which includes voyeurism and revenge porn, remained the most common form of tech-enabled sexual violence, with 54 cases last year, said Aware.