There are actually two sides to this.
First: yes, autism increases one's risk of experiencing trauma, which is a necessary precursor to PTSD. Many (though not all) studies have found that autistic kids are more likely to be abused or neglected, and this risk is much higher for autistic kids who have an intellectual disability. Some studies place the prevalence as high as two thirds of autistic kids. There's also a much higher risk of bullying, with different studies finding between 50% up to almost 100% of autistic kids are bullied in at least once incident each year. Rates of trauma in autistic adults are unfortunately less well known. (That's another thing that I'm trying to capture in my study.) Finally, autistic people may face stressors that typically developing individuals don't such as increased social stressors, sensory overload, and distress from unexpected situations or changes. These can all increase the impact of traumatic events or in some cases be perceived as traumatic (Baladerian, Coleman, & Stream, 2013; Schroeder, Cappadocia, Bebko, Pepler, & Weiss, 2014).
Second: yes, autistic people may be more likely to develop PTSD once exposed to trauma. Risks of developing PTSD include existing mental health difficulties (comorbid disorders are very common in autism), a lack of social support (unfortunately very common in autism), and lower IQ or difficulties regulating emotions (which affect a significant portion of people with autism). There are concerns that differences in how autistic people process events also increase the risk of poor outcomes (Kerns, Newschaffer, & Berkowitz, 2015).
As for coping mechanisms, therapy helps a lot. Learning to ground can help to manage flashbacks or panic. The usual -- stay healthy physically, obtain a strong support system if you can, try to manage stress without falling too far into avoidance -- also apply.