"I'm thinking, 'I want them to be safe', and I don't want the same thing happening again, because it can happen so easily," he said.
Mr Cromb lost his brother to suicide in 2012, and made an attempt on his own life in the aftermath - cyberbullying burdening both their lives. His brother David Jade Cromb, known as 'DJ', was 14 at the time.
"It wasn't until a month later that we found out a big factor of it had been cyberbullying," Mr Cromb said, adding that the bullying had been continuous.
"Eventually it just got a bit much for him. He just didn't talk to anyone, didn't tell any of us."
The 21-year-old president of the Otago Polytechnic Students' Association said: "I was 16 at the time and it was enough to go through processing the fact that my little brother would do that, but then to find out that somebody else had been involved in the cause for it.
"I've moved on from what he [DJ] has done, but that's still the part I've never moved on from, knowing that somebody else was [bullying him] secretly."
The situation was made more difficult because living in the small rural Otago town of Ranfurly meant he was forced to see his brother's bully every day at school.
"I couldn't escape him."
When he tried to find someone to talk to he received abusive text messages and online harassment. He ended up in Dunedin Hospital and eventually received counselling.
Mr Cromb's experience prompted him to take up positions with university and student organisations to "get the message out and tell people they need to talk about it and we need to sort it".
"I know it's not an easy conversation to have, but it's one that we desperately need to be having."
Just because you can't see it, doesn't mean it's not happening.
He advised anyone suffering cyberbullying to talk to someone about it from the beginning.
"It may not seem significant now when it starts, but you need to talk to somebody. Even if it's just a friend at that stage, or a staff member or parent or an aunty or uncle, just somebody that you trust.
"It's good to talk about it and get it out, because if you just bottle it all up it eventually can just become too much.
"No matter how horrible or dark it feels at the moment, you can get through it, you just need support and you need to just take your time."
And he urged cyberbullies to think about what they're doing and the hurt they're causing someone.
"Just because you can't see it, doesn't mean it's not happening," he said. "For whatever reason they're doing it, even if it's just to make themselves feel better about something in their own lives, that 5 minutes of feeling better, is it really worth the pain they can cause others and other people's families that will last a lifetime?
"And if it gets to the point where they [the victim] take their own life, it's the effects that it has on their friends and family.You never get over it, you spend every single day of your life wondering about it.
"I've got my first child on the way [with fiancee Summer McLeod] and every day I wonder, 'what would it be like if my brother was still here and he could be a part of this?'. My little sister turned 14 earlier this year, so she is now the same age as what he was, and the age that we all remember him at, so every single day is a struggle in one form or another, there's always a reminder somewhere."
Where to get help:
• In an emergency: call 111
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633, or text 234 (available 24/7) or talk@youthline.co.nz or live chat (between 7pm and 11pm) http://livechat.youthline.co.nz/mibew/chat?locale=en&style=youthline
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155 (weekdays 11am to 5pm)
• NetSafe: 0508 NETSAFE (0508 638 723), www.theorb.org.nz
How parents can stop cyberbullying:
• Understand where your kids are going online, what they are doing and who they are talking to.
• Spend time in your child's online world.
• Accept and acknowledge how important technology is to your child.
• Don't ask your child if they're being cyberbullied. Use their language - have they seen mean texts circulating, humiliating photos or messages on others' Facebook walls?
• Don't downplay covert bullying. Don't dismiss it saying "don't worry ... it doesn't matter if you've been left out" or "just ignore the bullying". This tells the child that you don't take their situation seriously and can even convey that it's normal for others to treat them this way.
• Make it clear cyberbullying will not result in phone or internet access being taken away. Discuss this with your child and reassure them that's not how you'll deal with it.
• Teach your kids how to be good cyber citizens before they are in Year 4, when they may begin to venture online.
• Much of cyberbullying and face-to-face bullying is learned behaviour. Look at what behaviours you're modelling to your kids. Is sarcasm and point-scoring part of your family culture?
• Don't contact the other child but tell the school principal.
